To see the other types of publications on this topic, follow the link: Pathogenic bacteria.
Dissertations / Theses on the topic 'Pathogenic bacteria'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Pathogenic bacteria.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Château, Maarten de. "Functional, structural and evolutionary studies on a family of bacterial surface proteins." Lund : Dept. of Cell and Molecular Biology, Lund University, 1996. http://catalog.hathitrust.org/api/volumes/oclc/38947242.html.
Full text
2
Kearney, Theresa Elizabeth. "Survival of pathogenic bacteria in anaerobic digesters." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334706.
Full text
3
Kim, Hyung Joo. "Electrochemical detection and enumeration of pathogenic bacteria." Thesis, King's College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244045.
Full text
4
Salmon, Richard Michael. "Structural studies on proteins from pathogenic bacteria." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/3287/.
Full text
5
Davids, Wagied. "Causes of Substitution Frequency Variation in Pathogenic Bacteria." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4838.
Full text
6
Lövkvist, Lena. "Receptor Interactions Between Pathogenic Bacteria and Host Cells." Doctoral thesis, Uppsala University, Department of Medical Biochemistry and Microbiology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7782.
Full textAbstract:
This thesis focuses on host and pathogen specific interactions during invasive disease. We have investigated the role and impact of different virulence factors of Neisseria gonorrhoeae, N. meningitidis and Streptococcus pyogenes on host epithelial cells and in vivo.
N. gonorrhoeae cause the sexually transmitted disease gonorrhoea and N. meningitidis is the most common cause of bacterial meningitis and may be leathal to the host within hours of infection. The neisserial type IV pili were shown to have an important impact on host cells for the induction of pro-inflammatory and other cellular defence transcriptional responses. Furthermore, N. meningitidis generally induced an earlier response compared to N. gonorrhoeae, probably as a result of the meningococcal capsule. The role of N. meningitidis serogroup B lipooliogsaccharide was investigated during invasive disease. Bacterial invasion of host cells and blood survival as well as virulence in vivo was dependent on the integrity of the LOS structure.
S. pyogenes may cause a variety of diseases ranging from uncomplicated diseases such as 'strep-throat' to more severe invasive diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. S. pyogenes ScpC protease degrade interleukin 8 during necrotizing fasciitis. We investigated the role of ScpC in systemic disease and observed enhanced virulence by bacteria unable to degrade IL-8. Following an intravenous infection of mice pro-inflammatory cytokines and complement activation was induced by the ScpC negative mutant compared to the wild-type and correlated with higher bacteremia. These data indicate that the precense of the ScpC protease has an important impact on the host for the outcome of streptococcal sepsis. Another phagocytic escape mechanism of S. pyogenes is their ability to coat themselves with host proteins. We observed that released complement control protein, CD46, bound to the streptococcal cell surface. CD46 has been shown to interact with the streptococcal M protein and have now been found to bind to the surface of the bacteria in a growth phase dependent manner. We observed a more aggressive disease development in CD46 transgenic mice after an intravenous infection with an M6 serotype, resulting in higher mortality of CD46 transgenic mice compared with control mice. These data indicate that CD46 may confer a protection to the streptococci during early stage of systemic infection and contributes to the understanding of immune evsion of S. pyogenes.
7
Abd, Hadi. "Interaction between waterborne pathogenic bacteria and Acanthamoeba castellanii /." Stockholm, 2006. http://diss.kib.ki.se/2006/91-7140-569-0/.
Full text
8
Lövkvist, Lena. "Receptor interactions between pathogenic bacteria and host cells /." Uppsala : Acta Universitatis Upsaliensis : Uppsala universitetsbibliotek [distributör], 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7782.
Full text
9
Chan, Anson Chi-Kit. "Iron transport in two pathogenic Gram-negative bacteria." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/32406.
Full textAbstract:
Campylobacter jejuni and Escherichia coli strain F11 are two Gram-negative pathogens with a versatile armament of iron uptake systems to cope with the fluctuating host nutrient environment. Our current understanding of Gram-negative iron uptake systems focuses heavily on a prototypical scheme involving a TonB-dependent outer membrane receptor and an ABC transporter, with little knowledge on systems that do not fall neatly into this paradigm. The primary focus of this thesis is the characterization of three such atypical iron uptake proteins from C. jejuni (ChaN and P19) and pathogenic E. coli (FetP).
C. jejuni ChaN is a 30 kDa, iron-regulated lipoprotein hypothesized to be involved in iron uptake. The crystal structure of ChaN reveals that it can bind two cofacial heme groups in a pocket formed by a ChaN dimer. Each heme iron is coordinated by a single tyrosine from one monomer and the propionate groups are hydrogen bonded by a histidine and a lysine from the other monomer. Analytical ultracentrifugation studies demonstrate heme-dependent dimerization in solution. Cell fractionation of C. jejuni shows that ChaN is localized to the outer membrane. Based on these findings, the predicted in vivo role of ChaN in iron uptake is discussed.
C. jejuni cFtr1-P19 and E. coli FetMP are homologous iron-regulated systems also proposed to be iron transporters. Through growth studies in both organisms, we show that P19 and FetMP are required for optimal growth under iron-limited conditions. Furthermore, metal binding analysis demonstrates that recombinant P19 and FetP bind both copper and iron. Dimerization of P19 is shown to be metal dependent in vitro and is detected in vivo by cross-linking. Through x-ray crystallography, we have determined the structures of P19 and FetP with various metals bound, thus revealing the locations of the highly conserved copper and iron binding sites. Additionally, the crystal structure of FetP reveals two copper positions in each binding site that is likely functionally important. Through mutagenesis, residues contributing to the alternative copper positions were identified. Together, these studies provide insight into the mechanism of iron transport by the two systems and allow for the development of functional models.
10
Hitchen, Paul Gareth. "Structural analysis of lipo-oligosaccharides from pathogenic bacteria." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268463.
Full text
11
Saunders, Jane Elizabeth. "Structure-function studies on EPSP from pathogenic bacteria." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405133.
Full text
12
Saramago, Ana Margarida Teixeira. "The Relevance of Ribonuclease III in Pathogenic Bacteria." Doctoral thesis, Universidade Nova de Lisboa. Instituto de Tecnologia Química e Biológica, 2013. http://hdl.handle.net/10362/12027.
Full textAbstract:
Dissertation presented to obtain the Ph.D degree in Biology.Ribonucleases (RNases) are key factors in the control of all biological processes, since they modulate the stability of RNA transcripts, allowing rapid changes in gene expression. Some RNases are up-regulated under stress situations and are involved in virulence processes in pathogenic microorganisms. RNases also control the levels of regulatory RNAs, which play very important roles in cell physiology.(...)
13
Arrojado, Cátia Susana Garrido Lobo. "Inactivation of fish pathogenic bacteria by cationic porphyrin." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/884.
Full textAbstract:
Mestrado em MicrobiologiaA importância da aquacultura tem vindo a aumentar de modo a compensar a progressiva redução mundial de peixes em ambiente natural. No entanto, esta indústria sofre frequentemente de elevadas perdas financeiras resultantes do desenvolvimento de infecções nos peixes causadas por microrganismos patogénicos, incluindo bactérias resistentes a antibióticos. Isto gera a necessidade de criar estratégias de controlo de infecções microbianas nos peixes que sejam benéficas para o ambiente, de modo a controlar a tornar a indústria e produção de peixe em aquacultura mais sustentável. A terapia fotodinâmica antimicrobiana tem surgido como um método alternativo para o tratamento de doenças e para evitar o desenvolvimento da resistência aos antibióticos por parte das bactérias patogénicas. Esta terapia consiste na utilização de um fotossensibilizador que absorve luz visível, na presença de oxigénio, levando a formação de espécies altamente citotóxicas que inactivam os microrganismos. O objectivo deste trabalho foi investigar o efeito fotodinâmico de bactérias Gram (-) (Vibrio anguillarum Vibrio cholerae, Vibrio, Aeromonas salmonicida, Photobacterium damselae damselae, Photobacterium piscicida damselae, Escherichia coli e Pseudomonas sp) e Gram (+) (Enterococcus faecalis e Staphylococcus aureus), isoladas de uma aquacultura da Ria de Aveiro (Portugal). Foi usada a porfirina catiónica livre Tri-Py+-Me-PF a concentração de 5.0 mM, e irradiação por exposição a luz branca artificial (40 W m-2) durante 270 minutos. O efeito da terapia fotodinâmica na estrutura da comunidade bacteriana total e na abundância de bactérias cultiváveis da aquacultura foi também avaliado O impacto do tratamento fotodinâmico na abundância dos isolados bacterianos e na comunidade bacteriana cultivável da aquacultura foi avaliado através do número de unidades formadoras de colónias (UFC) após sementeira em placas de agar. Os efeitos ao nível da estrutura da comunidade bacteriana foram avaliados por "denaturing gel gradient electrophoresis (DGGE)". A exposição ao derivado porfirínico na presença de luz branca resultou numa diminuição de 7-8 log na abundância dos isolados bacterianos. A abundância de bactérias cultiváveis nas amostras de água provenientes do sistema de aquacultura foi também afectada, mostrando um decréscimo até 2 log na sobrevivência das células bacterianas. Porém, a taxa de inactivação variou significativamente nos diferentes períodos de amostragem. Os perfis de DGGE revelaram uma diminuição da diversidade da comunidade bacteriana total da água da aquacultura com a aplicação do tratamento fotodinâmico. Os resultados sugerem que a terapia fotodinâmica antimicrobiana pode ser considerada como um novo método para o controlo de infecções bacterianas em peixes em aquacultura, contudo como em regimes semi-intensivos e extensivos a comunidade bacteriana não patogénica pode ser afectada, antes da implementação da terapia fotodinâmica devendo ser feita uma avaliação rigorosa das implicawes ao nível do ecossistema. ABSTRACT: Aquaculture is assuming an increasing importance for the compensation of progressive worldwide reduction of natural fish stocks. Fish farming often suffer heavy financia1 losses resulting from fish infections caused by microbial pathogens, including multidrug resistant bacteria. Therefore, more environmentally-friendly strategies to control fish infections are urgently needed, in order to make aquaculture industry more sustainable. Antimicrobial photodynamic therapy (aPDT) has emerged as an alternative to treat diseases and prevent the development of antibiotic resistance by pathogenic bacteria. This therapy involves the use of a photosensitizer that absorbs visible light, in the presence of oxygen, leading to the formation of highly cytotoxic species that inactivate microorganisms. The aim of this work was to investigate the photodynamic inactivation of Gram (-) (Vibrio anguillarum, Vibrio parahaemolyticus, Aeromonas salmonicida, Photobacferium damselae damselae, Photobacterium damselae piscicida, Escherichia coli and Pseudomonas sp.) and of Gram (+) (Enterococcus faecalis and Sfaphylococcus aureus) bacteria isolated from an aquaculture system of Ria de Aveiro (Portugal). A free cationic porphyrin Tri-Py+-Me-PF at 5.0 mM was used and the irradiation regime consisted of artificial white light (40 W. m-2) for 270 minutes. The effect of the photodynamic process on the total bacterial community structure and on the abundance of cultivable bacteria from the aquaculture system was also evaluated. Photodynamic inactivation of bacterial isolates and cultivable bacteria was assessed by the number of colony forming units (CFU) in agar plates. The impact of photodynamic treatment in the total bacterial community structure of the aquaculture plant was evaluated by denaturing gel gradient electrophoresis (DGGE).The results showed that, in the presence of porphyrin derivative d tri-Py+-Me-PF, the growth of bacterial isolates was inhibited, resulting in a decrease of = 7-8 log after 270 minutes of irradiation. Total cultivable bacteria from the aquaculture were also considerably affected, showing decreases up to = 2 log on cell survival by the photodynamic treatment. However, the inactivation rate varied significantly with the sampling period. DGGE profiles revealed a decrease in the diversity of the total bacterial community of the aquaculture water upon photodynamic treatment. Results indicate that photodynamic antimicrobial therapy can be regarded as new approach to control fish infections in aquaculture systems, but as non pathogenic microbial community of extensive and semi-intensive aquaculture systems can also be affected, a careful evaluation must be done before aPDT implementation in these systems.
14
Felts, Richard Levi. "Structural studies of acid phosphatases from pathogenic bacteria." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4857.
Full textAbstract:
Thesis (Ph.D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 23, 2009) Vita. Includes bibliographical references.
15
Habeeb, Fatema. "Bacteria-cytokines interactions : effect of normal bacterial flora of pathogenic bacteria on pro-inflammatory cytokines production in human blood." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501921.
Full text
16
Manning, Paul Alexander. "Bacterial cell surfaces and pathogensis : publications 1975-1998 /." Title page, contents and summary only, 1998. http://web4.library.adelaide.edu.au/theses/09SD/09sdm284.pdf.
Full text
17
Bryant, Josephine Maria. "Evolutionary genomics of pathogenic mycobacteria." Thesis, University of Cambridge, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708462.
Full text
18
O'Hara, Heather Marie. "Comparison of the different spectra of some selected bacteria." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/27161.
Full text
19
Abulreesh, Hussein Hasan. "Waterfowl, faecal indicators, and pathogenic bacteria in amenity ponds." Thesis, University of Hull, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421986.
Full text
20
Misciattelli, Natalia. "Control of pathogenic bacteria in marine larval culture systems." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311387.
Full text
21
Holmes, Ashleigh. "Characterising virulence factors from pathogenic bacteria using fluorescent reporters." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3317/.
Full textAbstract:
Protein translocation systems are invaluable to pathogenic bacteria, facilitating the display of virulence factors on their surface or their release into the extracellular environment. Some protein export systems are ubiquitous and essential to cell survival whereas others are horizontally acquired on prophages or pathogenicity islands (PAI), in many cases providing the bacterium with pathogenic advantages. For the majority of the known protein export systems, their structure, function and secreted substrates have been characterised, yet some proteins have been identified that are secreted via unknown mechanisms. Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is an important cause of human foodborne disease worldwide. The pathogenesis of this bacterium is mainly attributed to the secretion of toxins and the presence of a Type III Secretion System (T3SS). The T3SS can translocate bacterial proteins, known as effectors, into the host cell which mediate an effect culminating in the formation of a characteristic attaching and effacing (A/E) lesion. This system is encoded on a horizontally acquired PAI termed the locus of enterocyte effacement (LEE). The LEE not only encodes the T3SS apparatus but also several effectors secreted by the system and transcription factors which regulate its expression. However, it was recently found that T3SS not only secretes LEE encoded effectors but can also secrete proteins encoded on other prophages present in the EHEC genome. Characterisation of these non-LEE encoded effectors is ongoing and this study investigates the expression, regulation and function of non-LEE encoded effector H1 (NleH1) and H2 (NleH2). NleH1 and NleH2 are secreted by the T3SS but are encoded on different prophages. This study demonstrates that expression of NleH1 and NleH2 is induced in the same in vitro conditions which stimulate the expression of the LEE but is diminished upon initial host cell contact in vitro. Transcription of nleH1 and nleH2 is dependant upon factors specific to E. coli O157:H7 and these factors are regulated by LEE encoded regulators Ler and GrlA, as they have a positive effect on nleH transcription. NleH1 and H2 are predicted serine/threonine protein kinases and are able to autophosphorylate. Yeast two hybrid screening and 2D differential gel electrophoresis did not elucidate a eukaryotic protein binding partner of NleH1 or NleH2. Transfection assays show that they do not have a significant effect upon NF-κB activation in vitro. Determining the expression, regulation and function of non-LEE encoded effectors contributes towards further understanding of how this pathogen causes disease. Streptococcus pneumoniae, also known as the pneumococcus, is another globally important human pathogen. It is a very diverse pathogen, with over 90 capsular serotypes and is naturally competent for DNA uptake. Pneumococcal pathogenesis is facilitated by the production of a pore-forming toxin, pneumolysin. Pneumolysin’s activities in pneumococcal pathogenesis extend beyond its cytolytic function as it can also activate the complement pathway and modulate the host cytoskeleton. Pneumolysin is a member of a conserved family of toxins known as the cholesterol dependant cytolysins but differs due to the lack of a secretion signal peptide within its sequence. This indicates that it is not secreted from the bacterium however it has been reported that some strains can release pneumolysin in a cell lysis-independent manner. Additional to this, pneumolysin can also localise to the cell wall, and this localisation is not strain dependent. This study characterised codon-optimised N-terminally labelled pneumolysin constructs and applied them to assess the localisation of pneumolysin. In addition, the importance of autolysin and genes which are co-transcribed with Ply upon the localisation/secretion of pneumolysin was investigated by construction of a pneumococcal strain carrying an autolysin-pneumolysin fusion which naturally occurs in equine strains. These genes were not required for the translocation of pneumolysin or its association with the cell wall. Growth of this strain, and its isogenic parent, in vitro at a low density and low temperature resulted in the pneumolysin being detected in the broth culture. This indicates that pneumolysin can be released from the cell wall and that this action is not dependant upon the genes which were deleted in the mutant. The distribution of pneumolysin on the pneumococcal surface was assessed with immunofluorescence, and LumioTM substrate fluorescence, microscopy and found to have a general distribution. As a contribution to future pneumococcal research, codon-optimised fluorescent protein reagents were developed and can be used as reporters for gene expression and protein localisation.
22
Twing, Katrina Irene. "Pathogenic Epsilonproteobacteria and fecal indicator bacteria in Delaware waterways." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 50 p, 2009. http://proquest.umi.com/pqdweb?did=1885607691&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
23
Reyna-Granados, Javier Rolando. "Control of Foodborne Pathogenic Bacteria Using Natural Plant Antimicrobials." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228511.
Full textAbstract:
Foodborne pathogens are a threat to public health worldwide. Because many consumers prefer natural compounds to synthetic additives, research on safe plant-derived compounds with antimicrobial activity against foodborne pathogens is vital. The aim of this investigation was to evaluate the antimicrobial activities of plant essential oils (oregano, cinnamon, lemongrass), their active components (carvacrol, trans-cinnamaldehyde, citral) and plant-extracts such as green tea, apple skin extract, black and decaffeinated black tea, grapes seed and pomace extracts against foodborne bacteria. Salmonella enterica serotype Typhimurium DT104, and serotype Newport, were selected conducting an antibiotic screening on 23 Salmonella isolates using seven antibiotics to determine antibiotic resistance. Listeria monocytogenes (strain 101M; beef and pork sausage isolate; resistant to antimicrobials in past investigations) was included to represent gram-positive bacteria. Escherichia coli O157:H7 virulent isolates (932- apple juice isolate; ATCC 35150- human isolate; F4637- sprouts isolate; used as a cocktail) were selected after conducting a Multiplex PCR over nine E. coli O157:H7 isolates to detect shiga-toxin 1 and 2 genes. All antimicrobials were evaluated in vitro in phosphate buffered saline. In general, all pathogens were more susceptible to essential oils and their active components, than powder extracts. The most active antimicrobials from each category were directly applied on foods. The activity of oregano oil (0.5%) and green tea (3%) was evaluated against S. Typhimurium on chicken and S. Newport on tomatoes and sprouts, and the results showed that oregano oil was more effective. In addition, baby spinach leaf samples inoculated with green fluorescent protein labeled S. Newport were examined under confocal scanning laser microscope before and after antimicrobial treatments. Antimicrobial experiments against L. monocytogenes on sprouts, ham and bologna, carvacrol at 0.5% and grape seed extract at 3% were used and carvacrol showed better activity. Antimicrobial activity against E. coli O157:H7 was tested on romaine lettuce, spinach and ground beef using oregano oil at 0.5% and green tea at 3%. Both compounds were effective showing no recovery of E. coli O157:H7 from lettuce and spinach; however, was not reduced in ground beef. Antimicrobial plant compounds have the potential for reducing foodborne pathogenic bacteria on/in various foods.
24
Ferrara, Luana. "Structural and functional studies of porins from pathogenic bacteria." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/15639.
Full textAbstract:
Multi-drug resistant bacteria have become a real threat to public health worldwide. Gram-negative bacteria, in particular, have shown high level of antibiotic resistance due to the presence of an additional membrane, known as outer-membrane (OM), that acts as an extra barrier. Most antibiotics enter the cells via a particular class of outer-membrane proteins (OMPs) known as porins. Porins are β-barrel channels that allow the passive diffusion of hydrophobic compounds. The porins are known to select against molecules on the basis of size and charge. When exposed to antibiotics, bacteria can modify the OM permeability by altering their porins profile. Mutations affecting the size and conductivity of the pore channel, and modification of the level of porins expression are just a few examples of how the bacteria can decrease the influx of antibiotics. In order to better understand their interaction with antibiotics, this thesis presents structural and functional studies on porins from pathogenic bacteria. The structure of the natively expressed major outer-membrane protein (MOMP) from Campylobacter jejuni was determines, revelling the presence of a calcium-binding site inside the channel. Electro-physiology and in silico modelling analysis have shown to be important for the stability and the function of the protein. Omp50 from C. jejuni was expressed in E. Coli and its tyrosine kinase activity was analysed in vitro. Finally the structures of the two major porins from Enterobacter aerogens were determined and compared to their orthologs within the Enterobacteriaceae family. Further, a liposome-swelling assay (LSA) was used to deter-mine the rate of permeation of clinically relevant antibiotics through a series of porins. Combining these data allow a more detailed molecular understanding of translocation.
25
Foo, Chuen-hing, and 符傳興. "Bacteremia due to Elizabethkingia and related species." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208519.
Full textAbstract:
Elizabethkingia spp. is a gram-negative, non-fermenting rod bacterium that is frequently implicated in hospital outbreaks. Elizabethkingia has a high rate of resistance to antibiotics and a shortage of effective parenteral antibiotics usually occurs in intensive care units. Infection includes neonatal sepsis and meningitis. Recently, a new species of Elizabethkingia, which is closely related to E. meningoseptica ATCC 13253 and E. miricola GTC862, was reported as a human pathogen in Central Africa and named E. anophelis. Our investigation involved 27 Elizabethkingia clinical isolates, which were fully identified through phenotypic and genotypic typing. The isolates were identified as E. meningoseptica by VITEK 2 (bioMereux) and Phoneix (Beckton Dickinson) automated bacterial identification systems. We then re-identified the isolates by 16S rRNA gene sequencing; 23 of the 27 strains were identified as E. anophelis and one was identified as E. miricola instead of E. meningoseptica. Subsequently, we evaluated the performance of the Bruker MALDI-TOF MS system for identification of the E. anophelis strains; many were misidentified as E. meningoseptica or were unidentified. All of the strains were correctly re-identified as E. anophelis when the original Bruker database was expanded with the inclusion of 10 E. anophelis clinical isolates and a standard 〖R26 〗^T strain. We also analysed 23 E. anophelis clinical isolates by biochemical tests, antimicrobial susceptibilities tests and pulsed-field gel electrophoresis. From the biochemical investigation of all isolates and type strain, showing that the conventional biochemical tests are not reliable to differentiate E. anophelis from other Elizabethkingia spp. More than 75% of the isolates tested were susceptible to cotrimoxazole, ciprofloxacin, and cefoperazone-sulbactam, however they were all resistant to aminoglycosides and beta-lactam drugs except one strain. At the PFGE investigation all the strains were not clonally related as shown by PFGE and displayed distinct PFGE fingerprints.published_or_final_version
Medicine
Master
Master of Medical Sciences
26
Parry, R. W. H. "Xanthomonas infections of rice : The involvement of bacterial extracellular polysaccharide." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354044.
Full text
27
Hapeshi, Alexia. "Chromosomal and plasmid determinants of Rhodococcus equi virulence." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/17281.
Full textAbstract:
Rhodococcus equi is a soil-dwelling actinomycete with the ability to cause pyogranulomatous infections in different animal species and people. Young foals are particularly susceptible and develop a severe pulmonary illness known as rhodococcal pneumonia. The infection is endemic in many horse-breeding farms worldwide and poses a major challenge to the equine industry, as there is no commercial vaccine available. R. equi is a facultative intracellular pathogen. Intracellular survival in macrophages and hence virulence depends on the presence of large plasmids that carry a set of genes encoding virulence-associated proteins (Vaps) of largely unknown functions. Virulence plasmids are of different types and appear to determine host-specific infectivity for horses, pigs and cattle. In this thesis, I explored bacterial chromosomal factors that contribute to the virulence of R. equi. Previous microarray transcription profiling work from the laboratory showed that housekeeping metabolic genes from the R. equi chromosome were co-opted to serve a virulence function via co-regulation with plasmid virulence genes. Here, I identified a further virulence plasmid-co-expressed metabolic chromosomal locus with a key role in R. equi pathogenesis. The identified locus, gltAB1, encodes an NADPH-dependent glutamate synthase required for ammonia assimilation under low nitrogen conditions. Reverse-transcription quantitative rea-ltime PCR confirmed that gltAB1 was co-expressed with the vap genes from the plasmid whereas a homologous chromosomal locus encoding a second NADPH-dependent glutamate synthase, gltAB2, was not. In-frame deletion mutants were constructed and their virulence analysed. gltAB1 but not gltAB2, was found to be involved in virulence and required for intracellular proliferation in J774A.1 macrophages. The ΔgltAB1 mutant showed significant attenuation in vivo in a mouse infection model, in contrast to the ΔgltAB2, which behaved like the wild type. The ability of the ΔgltAB1 mutant strain to act as a live attenuated vaccine was tested in experiments in BALB/c mice. The mutant conferred protection against subsequent challenge of the animals with wild-type virulent bacteria, thus identifying a novel candidate vaccine for the control of R. equi pneumonia in foals. Furthermore, this thesis describes studies of the bovine-type plasmid, previously sequenced in our laboratory. The purpose of this work was to determine if VapN, the bovine-type allelic variant of the VapA protein encoded in the equine-type plasmid, was also essential for R. equi virulence. A plasmid-less derivative strain and a deletion mutant in the vapN gene were examined for their ability to proliferate in two different cell lines and to persist in BALB/c mice. These strains showed the same strong virulence attenuation observed with plasmid-less and ΔvapA strains derived from the equine isolate R.equi 103S, demonstrating that the bovine-type VapN protein also plays a central role in R. equi virulence. Additionally, the thesis includes preliminary work on approaches to explore the role and mechanism of Vap proteins in R. equi virulence. It also describes the construction of GFP-tagged R. equi strains for use in cell biological experiments and live imaging of infected cells.
28
Meyer, Hanna [Verfasser]. "Applying metabolomics to Gram-positive bacteria: Investigations on pathogenic and biotechnological relevant bacteria / Hanna Meyer." Greifswald : Universitätsbibliothek Greifswald, 2014. http://d-nb.info/1051066409/34.
Full text
29
VieBrock, Lauren. "ORIENTIA TSUTSUGAMUSHI ANKYRIN-REPEAT PROTEIN FAMILY TARGETING OF THE HOST ENDOPLASMIC RETICULUM." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/4023.
Full textAbstract:
Abstract
ORIENTIA TSUTSUGAMUSHI ANKYRIN REPEAT-PROTEIN FAMILY TARGETING OF THE HOST ENDOPLASMIC RETICULUM
By Lauren VieBrock, B.S.
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University
Virginia Commonwealth University, 2015
Director: Jason A. Carlyon, Ph.D.
Professor
Microbiology and Immunology
Scrub typhus is an understudied, potentially fatal febrile illness, which poses threat to one billion people annually in the Asia-Pacific region. The host-pathogen interactions that facilitate the intracellular survival of the etiologic agent, Orientia tsutsugamushi, are not well understood. The Orientia tsutsugamushi genome encodes a large number of ankyrin repeat-containing proteins (Anks), key virulence factors for other intracellular pathogens, as well as components for Type I (T1SS) and Type 4 secretion systems (T4SS), commonly used to deliver them. We sought to characterize the roles of the Anks in O. tsutsugamushi infection. In this study, we demonstrated that O. tsutsugamushi expressed all 20 anks and the genes for the T1SS, for which they are substrates. Many ectopically expressed Anks displayed a tropism for the host endoplasmic reticulum (ER). These
results suggest the importance of the Anks and the ER to Orientia tsutsugamushi pathobiology.
We demonstrated that O. tsutsugamushi tightly associated with the ER and induced ER stress and defects in protein secretion of its host cells. Therefore, we hypothesized that the ER-tropic anks expressed during the initial hours of infection are critical for establishing infection and do so by interacting with specific host cell targets to modulate host cell function to benefit intracellular survival. ER-tropic Ank4 was detected as expressed early in infection and was further characterized for its contribution to the alterations of the ER during infection. Bat3 was identified as a target of Ank4, and Ank4 expression correlated with a decrease in Bat3 protein levels, induction of ER stress, and defects in protein secretion. These effects were Ank4 F-box dependent, implicating polyubiquitination and proteosomal degradation of Bat3. As Ank4 colocalized with Bat3, a chaperone component of ER-associated degradation (ERAD) of misfolded proteins, ERAD function was measured in cells expressing Ank4. In an F-box dependent manner, Ank4 expression resulted in decreased degradation of a model substrate and indicated inhibition of the ERAD pathway. Similarly, we demonstrated that in O. tsutsugamushi infection, Bat3 levels were significantly reduced early in infection and ERAD degradation was inhibited. After several days of infection however, Bat3 levels and ERAD degradation had both recovered, suggesting temporal modulation of ERAD in infection. Taken together, these data suggest that O. tsutsugamushi has a large capacity to disrupt the host ER, exemplified by Ank4 mediated ERAD dysfunction by depletion of host Bat3.
30
Li, Huajing, and 李華菁. "Oral commensal/pathogenic bacteria-host cells crosstalk : immuno-inflammatory response, microenvironmental regulation and signaling mechanism." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208543.
Full text
31
Meaden, Sean McClarey. "The tri-trophic interaction of plants, pathogenic bacteria and bacteriophages." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/22133.
Full textAbstract:
The ecology and evolution of pathogens are key factors in predicting the severity and spread of disease, as well as treatment outcomes. However, the effects of multiple trophic levels that include host, microbial competitors and viruses are typically overlooked. In this thesis I develop our understanding of bacteria-phage coevolution, microbial dispersal and the role of the microbiome in disease. The results of these experiments have direct implications for phage therapy: the use of bacteriophages to treat bacterial infections. Firstly, I explore the risks of phage application in the environment and draw parallels with the misuse of antibiotics in selecting for bacterial resistance. I then demonstrate that the evolution of resistance to phages in a plant pathogenic bacterium is context-dependent. Notably, I find a fitness cost in plant infections that is absent when the bacteria are cultured solely in the laboratory. I then characterize four novel phages and use a simple laboratory based assay to predict their potential as phage therapy agents in an agricultural context. Next I show that reservoir species of plant hosts can affect the evolution of virulence, when bacteria are passaged on both a focal and distant host, but find no evidence of local adaptation. I also show that the evolution of such traits can occur in a parallel manner at the genetic level. I then determine a compositional shift in the microbiota associated with the symptoms of bleeding canker disease in Horse Chestnut trees across the length of the UK. Finally, I find an age-elated decline in bacterial species richness and evidence for niche-assembly theories by investigating bacterial dispersal in UK Oak trees in a single woodland.
32
Wang, Jiahui. "Modulation of phosphoinositide metabolism by intracellular pathogenic bacteria Listeria monocytogenes." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/modulation-of-phosphoinositide-metabolism-by-intracellular-pathogenic-bacteria-listeria-monocytogenes(1ba79d85-5369-4bc5-8d49-aea2ffc0a7ca).html.
Full textAbstract:
Listeria monocytogenes is a Gram-positive facultative intracellular bacterium with a wide ecological niche and causes a number of diseases in human and animals. It invades mammalian host cells and escapes from the vacuoles prior to replication in the host cell cytoplasm and infecting adjacent cells via actin-based mobility. Phosphoinositide (PIP) metabolism is essential to mammalian cells in signal transduction, actin remodelling, endosome dynamics and membrane trafficking. Modulation of host PIP metabolism by bacteria PIP phosphatases is important for pathogenicity and virulence of many human pathogens. In this study the function of two L. monocytogenes tyrosine and inositol phosphatases LipA and LipB were studied in vitro. The lipA and lipB deletion mutants generated in EGDe and InlA strains were not affected in invasion but were attenuated in intracellular growth in Caco-2 and Hela M cell lines but not in mouse macrophages. Deletion of lipA or lipB did not affect the actin polymerisation but caused reduced plaque number in the plaque assay. The turnover of five PIPs in Hela M cells during L. monocytogenes infection were studied by expression of fluorescent protein tagged domains that specifically recognizes individual PIPs. L. monocytognenes did not affect the metabolism of PI4P, PI(4,5)P2, PI(3,4,5)P3 but co-localised with PI3P at 1.5 hr post-infection and with PI(3,4)P2 at 6 hr to 24 hr post-infection. The PI(3,4)P2 effector protein lamellipodin was discovered to be recruited to actin-associated L. monocytogenes at 4 hr to 24 hr post-infection in Hela M cells. This discovery leads to the hypothesis of a novel mechanism of lamellipodin-dependant cell-to-cell spread. The lipA mutant was found to be attenuated in PI(3,4)P2 recruitment and therefore hypothesized to participate in the proposed lamellipodin pathway by converting PI(3,5)P2 into PI5P, leading to the activation of PI3K and subsequent production of PI(3,4)P2. LipB showed partial localisation at the Golgi complex when over-expressed in Hela M cells, and it was assumed to act mainly as a protein-tyrosine phosphatase. In summary, this study provides some evidence on L. monocytogenes modulating host PIP metabolism by the production of inositol phosphatases. It gives us a better understanding on the intracellular growth of this pathogenic bacterium, and on the interaction between host and parasite.
33
Jin, Terry David. "Fluorogenic 1,8-naphthalimide derivatives for the detection of pathogenic bacteria." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14156.
Full textAbstract:
Novel fluorogenic enzyme substrates were synthesized by the coupling of 6-hydrazinobenz[de]isoquinoline-1,3-diones with β-alanine for the detection of β-alanyl aminopeptidase-producing Pseudomonas aeruginosa. A secondary reaction was also utilized involving the condensation of the 6-hydrazinobenz[de]isoquinoline-1,3-diones with a range of aryl aldehydes to give the corresponding hydrazones as a means for obtaining more favourable fluorescence properties. The photophysical properties of the synthesized hydrazines and their hydrazide and hydrazone derivatives, were examined and they were also incorporated into Columbia agar in order to determine their potential for the detection of pathogenic bacteria. The synthesized hydrazides and coupled derivatives displayed good fluorescence properties, with an average Stokes’ shift of 67 nm. Incorporation of a secondary reaction with aldehydes enhanced the fluorescence properties, with the exception of hydrazones containing the 4-dimethylamino substituent. Hydrazones prepared from benzaldehyde and 4-chlorobenzaldehyde displayed greatly increased fluorescence intensity, with no bathochromic shift, while the hydrazones from cinnamaldehyde and p-anisealdehyde displayed a favourable bathochromic shift along with a slight increase in fluorescence intensity. Incorporation of the synthesized compounds into Columbia agar, however, did not have the expected effects, as the majority of observed fluorescence was seen to be due to the substrate, and not the fluorophore. A high degree of localization of fluorescence within bacterial cells was, however, observed, although longer chain N-substituents appeared to have bactericidal effects on the microorganisms tested.
34
Yeung, Shiu-yan, and 楊兆恩. "Update and evaluation of 16SpathDB, an automated comprehensive database for identification of medically important bacteria by 16S rRNA gene sequencing." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/193552.
Full textAbstract:
Identification of pathogens is one of the important duties of clinical microbiology laboratory. Traditionally, phenotypic tests are used to identify the bacteria. However, due to some limitations of the phenotypic tests, the bacteria may not be identified sometimes and cannot be identified promptly. 16S rRNA gene sequencing is a rapid and accurate method to achieve this target. It is especially useful for identify rare or slow growing bacteria. However, the interpretation of the 16S rRNA gene sequencing result is one of the challenging duties to laboratory technicians and microbiologists. Apart from the well known 16S rRNA gene databases such as Genbank, The Ribosomal Database Project (RDP-II), MicroSeq databases, Ribosomal Differentiation of medical Microorganism database (RIDOM), SmartGene IDNS, 16SpathDB is an automated and comprehensive database for interpret the 16S rRNA gene result. The 16SpathDB first version was established in 2011. In this study, 16SpathDB was updated based on the all clinical important bacteria present in the 10th edition of the Manual of Clinical Microbiology (MCM)(Versalovic. et al., 2011) into this new version of database, 16SpathDB 2.0. The database was evaluated by using 689 16S rRNA gene sequences from 689 complete genomes of medically important bacteria. Among the 689 16S rRNA gene sequences, none was wrongly identified by 16SpathDB 2.0, with 247 (35.8%) 16S rRNA gene sequences reported in only one single bacterial species with more than 98% nucleotide identity with the query sequence (category 1), 440 (63.9%) reported as more than one bacterial species having more than 98% nucleotide identity with the query sequence (category 2), 2 (0.3%) reported to the genus level (category 3), and none reported as “no species in 16SpathDB 2.0 found to be sharing high nucleotide identity to your query sequence” (category 4). 16SpathDB 2.0 is an updated, automated, user-friendly, efficient and accurate database for 16S rRNA gene sequence interpretation in clinical microbiology laboratories.published_or_final_version
Microbiology
Master
Master of Medical Sciences
35
Han, Bin. "Regulation of the synthesis of extracellular protease and cellulase enzymes in Xanthomonas campestris." Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316748.
Full text
36
Griffin, Blakeley. "A Study of the Polymicrobial Inhibitory Interactions Between Alcaligenes faecalis and Staphylococcus aureus." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/honors/579.
Full textAbstract:
Members of the Staphylococcus genus are found as a part of normal microflora in humans and can commonly be found on the skin or in the nasal cavity. However, these microorganisms can cause serious and life-threatening opportunistic infections when there is a break in the physical barrier of skin. These infections have become difficult to treat as resistant strains emerge, particularly Methicillin Resistant Staphylococcus aureus (MRSA). MRSA has become a commonly acquired nosocomial infection which is difficult to treat with conventional antibiotics of the blactam class. Even Vancomycin, a last resort antibiotic, has been ineffective on some infections. Furthermore, S. aureus readily forms biofilms on implanted medical devices which establishes a hardy and difficult to treat infection. These biofilms serve as a point of infection to the bloodstream. Research involving polymicrobial interactions and the inhibitory effects of bacterial-bacterial interactions could be a starting point for the discovery of a new therapeutic treatment for infections. It has been shown in our lab that Alcaligenes faecalishas inhibitory effects on Staphylococcus aureusplanktonic growth. Therefore, in this study, we wanted to examine 1) The mechanism by which A. faecalisinhibitsS. aureus growth and 2) how A. faecalisimpacts the various phases of S. aureusbiofilm growth. It was found that A. faecalislikely inhibits S. aureususing a physical mechanism that requires close contact, rather than using a secreted molecule. However, a Type VI secretion system could also produce similar results. Further research involving the formation of mutants to find the gene allowing A. faecalisto inhibit S. aureuswas started, but no viable mutants were created during the course of this research. A. faecaliswas found to inhibit the formation of S. aureus biofilm growth, but when added to a mature S. aureusbiofilm, the slow growth rate of A. faecaliscould not overtake the quickly replicating S. aureus. Further research in the polymicrobial interactions between S. aureus and A. faecaliscould lead to a finding of a new therapeutic target for antibiotics or the use of A. faecalisin infections.
37
Emmett, Warren Anthony. "Using oligonucleotide signatures to build a system for effective detection of pathogenic bacteria in metagenomic samples." Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-08112009-151918.
Full text
38
Gaviria, Cantín Tania Cristina. "Factores Gre de Salmonella enterica serovar Typhimurium, su papel en el control de la filosofía y patogenicidad." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/397788.
Full textAbstract:
El género Salmonella, está compuesto de bacterias Gram-negativas, no esporuladas, en forma de bacilo. Salmonella tiene importante relevancia a nivel de salud pública ya que es uno de los principales patógenos entéricos tanto en países desarrollados como en vías de desarrollo. En los casos de gastroenteritis notificados en España, Salmonella se posiciona en segundo lugar, después de Campylobacter. En este trabajo se utilizó como organismo modelo de estudio S. enterica serovar Typhimurium (S. Typhimurium), que en humanos causa salmonelosis, gastroenteritis caracterizada por diarrea inflamatoria, originada normalmente tras la ingestión de alimentos o agua contaminados. Los genes de virulencia de S. Typhimurium están localizados mayoritariamente dentro de islas de patogenicidad (SPI). Los genes codificados en la SPI-1 promueben la invasión de células eucariotas, la regulación de la expresión de los genes de la SPI-1 está mediada por HiIA codificada en el gen, hilA, presente en la misma SPI-1. HiIA activa la expresión de los genes que codifican para la síntesis de un sistema de secreción de tipo 3 (T3SS) encargado de secretar e inyectar proteínas efectoras dentro de la célula hospedadora. La expresión de hilA se encuentra bajo el control de unl bucle de regulación, comprendido por las proteínas HiID, HiIC y RtsA. HiID es el regulador predominante de este sistema, mientras que HiIC y RtsA se encargan de amplificar la señal de activación. Por su parte, los genes que contiene la SPI-2, están implicados en causar infecciones sistémicas y la proliferación intracelular de la bacteria. Los factores Gre son factores que regulan la elongación de la transcripción génica en procariotas. Son conocidos por promover la actividad endorribonucleotídica de la ARN polimerasa (ARNpol) cuando ésta se encuentra en un estado de pausa por retroceso causado durante la elongación de la transcripción. A pesar de que los factores Gre han sido bien caracterizados en otras enterobacterias como Escherichia coli, en Salmonella no existen estudios que describan el papel de los factores Gre en la fisiología celular. Así, el objetivo principal de esta tesis doctoral fue estudiar el papel de los factores Gre en la fisiología y patogenicidad de Salmonella. En este estudio describimos que los factores Gre forman parte de la compleja red reguladora de la expresión de los genes de la SPI-1 y SPI-2 de Salmonella. Los resultados obtenidos indican que los factores Gre de Salmonella son esenciales para la correcta expresión de las proteínas efectoras codificadas dentro de la SPI-1 (SipA, SipC y SipD) y fuera de ella (SopE), y que también juegan un papel importante en la motilidad de la célula bacteriana, fenotipos predominantes en la patogenicidad. Se pudo determinar que la regulación de la expresión de los genes de la SPI-1 y la SPI-2 por parte de los factores Gre, es a través de la regulación transcripcional del gen hilD. La regulación mediada por los factores Gre requiere de la región 3'UTR del gen hilD. Además demostramos que la actividad antipausa de la transcripción de los factores Gre es necesaria para la correcta expresi formación de biofilm en Salmonella. Esta regulación al parecer también es ejercida en una región UTR, en este caso en la región 5’UTR del gen csgD, y es independiente de la temperatura. En análisis transcriptómicos mediante la técnica de microarrays, se observó que los factores Gre de Salmonella estarían implicados en la correcta expresión de muchos de los genes adquiridos horizontalmente (HGT)
como son los genes presentes en las islas de patogenicidad, plásmidos y fagos. También se observó que existe un elevado número de genes distribuidos en diferentes categorías funcionales, que son corregulados por los factores Gre en conjunto con la proteína DksA, proteína que incrementa la fidelidad de la transcripción al disminuir la tasa de incorporación incorrecta de nucleótidos. Estos resultados indican que el patrón general de expresión génica de Salmonella es el resultado de una compleja interacción entre los factores Gre y la proteína DksA, que implica el control mutuo, competición por la unión a la ARNpol, y la acción similar u opuesta sobre la actividad de la ARNpol. Con los resultados presentados en esta tesis doctoral se puede concluir que los factores Gre forman parte de la compleja red de regulación de los genes de virulencia de Salmonella.ón de hilD.Gre factors regulate gene transcription elongation in prokaryotes. In Escherichia coli they promote cleavage of the nascent RNA transcript within the elongation complex when the RNA polymerase is paused by a backtracking. Although the Gre factors have been characterized in other enterobacteria, in Salmonella there are not studies about their role in cellular physiology. The main objective of this thesis was to study the role of Gre factors in physiology and pathogenicity of Salmonella. In this study we describe Gre factors that are part of the complex regulatory network of gene expression of Salmonella pathogenicity island-1 (SPI-1) and SPI-2. The results indicate that Gre factors are pivotal in the control of predominant phenotypes in pathogenicity. They are essential for the correct expression of effector proteins encoded within (SipA, SipC and SipD) and outside SPI-1 (SopE), and they also play an important role in motility of the bacterial cell. It was determined that the regulation of gene expression of SPI-1 and SPI-2 by Gre factors is through transcriptional regulation of hilD gene. Regulation mediated by Gre factors requires hilD 3'UTR region. We demonstrated that Gre antipausa activity during transcription is necessary for the correct expression of hilD. It was also observed that Gre factors play an important role in transcriptional expression of csgD, main regulator of biofilm formation in Salmonella. This regulation is also apparently exerted through the 5'UTR region of the csgD gene, and is temperature- independent. In transcriptome analysis using Microarray, it was observed that Gre factors are implicated in the correct expression of many horizontally transferred genes (HGT) such as genes present in pathogenicity islands, plasmids and phages. It was also noted that there is a large number of genes distributed into different functional categories, which are co-regulated by Gre factors together with DksA protein, a protein that increases the accuracy of the transcript to decrease the rate of nucleotide missincorporation. These results indicate that the overall pattern of gene expression of Salmonella is the result of a complex interaction between Gre factors and DksA protein, involving the mutual control, competition for binding to ARNpol, and similar or opposite action on ARNpol activity. We can conclude that Gre factors are part of complex regulatory network of virulence genes of Salmonella.
39
Smith, Hannah. "Wild Australian shorebirds as reservoirs of pathogenic bacteria and antimicrobial resistance." Thesis, Federation University Australia, 2020. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/179783.
Full textAbstract:
Many existing and emerging diseases of humans are of zoonotic origin. In addition, the development of antimicrobial resistance (AMR) presents a serious risk for hospitals, agriculture, and the community. Habitat loss and degradation are forcing many wild animal populations into closer contact with human populations, presenting opportunities for the introduction and transmission of bacterial diseases. In Australia, many shorebird species undertake yearly migrations to and from breeding grounds in the high Artic, and during their migrations they pass over one-third of the human population. To determine if shorebirds are reservoirs of pathogenic bacteria the research presented in this thesis investigated the presence of three common enteric bacterial pathogens in twelve species of wild Australian shorebird; followed by AMR profiles of isolates, and genetic characterisation of selected isolates. In total, 1022 individual birds were sampled across three Australian states and tested for the presence of three potentially zoonotic pathogens; Escherichia coli, Enterococcus spp., and Salmonella spp. Two-hundred and six E. coli, 266 Enterococcus, and 20 Salmonella isolates were recovered, with AMR observed in 42% of E. coli isolates, 85% of Enterococcus isolates, and 10% of Salmonella isolates. Sedentary birds were more likely to carry AMR bacteria than migratory birds. A selection of E. coli isolates (n=16) underwent whole genome sequencing, and analysis of their genomes indicated a high level of genetic diversity with each isolate having a unique serotype. A total of 33 recognised virulence genes and eight AMR genes were detected. An important food-borne pathogen, Salmonella enterica serovar Hvittingfoss, was also recovered from one species of bird. This study shows that wild shorebirds can carry pathogenic enteric bacteria. While migratory birds may be less likely to harbour AMR bacteria relative to sedentary birds, they pose the potential to act as vectors for enteric and foodborne pathogens.Doctor of Philosophy
40
Butterworth, Lynne Angela. "Evaluation of novel enzyme substrates for the detection of pathogenic bacteria." Thesis, Durham University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400674.
Full text
41
Morley, Robert James. "An investigation into the interactions between pathogenic bacteria and Acanthamoeba polyphaga." Thesis, University of Bath, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411034.
Full text
42
Balasubramanian, Srikkanth [Verfasser], and Tobias [Gutachter] Ölschläger. "Novel anti-infectives against pathogenic bacteria / Srikkanth Balasubramanian ; Gutachter: Tobias Ölschläger." Würzburg : Universität Würzburg, 2018. http://d-nb.info/1162444509/34.
Full text
43
Kondacs, Laszlo. "Novel substrates for the improved detection and identification of pathogenic bacteria." Thesis, University of Sunderland, 2018. http://sure.sunderland.ac.uk/10222/.
Full textAbstract:
Many diseases are caused by pathogenic bacteria. A key example of this is sepsis, which is mostly caused by staphylococci and Gram-negative bacteria. In addition, the highly resistant ESKAPE pathogens are responsible for the majority of hospital acquired infections. In order to treat bacterial infections effectively, and to avoid promoting bacterial resistance against antibacterial drugs, the correct agents must be used, for which in turn the detection and identification of pathogenic strains is essential. This research aims to develop selective chromogenic culture media, by introducing new antibacterial agents for the improved selectivity and new chromogenic substrates for selective visualisation of certain bacterial strains. The intention of the major part of this work was to inhibit the growth of commensal bacteria in clinical samples, as they mask the growth of the infection-causing bacteria. New and known compounds were prepared for 3 evaluation as alanine racemase inhibitors. The compounds were tested on a range of clinical pathogenic and non-pathogenic bacterial strains. The molecules developed were based on the amino acid alanine and utilised bioisosteres and other replacements for the carboxylic acid moiety. Key compounds targeted included alanylmethanesulfonamide 27-L, 1-aminoethyl5-oxo-1,2,4-oxadiazole 33-L and 1-aminoethyltetrazole 32a-L. Each compound was tested initially as the alanyl-X dipeptide form. While most of the alanine bioisosteres were known structures, their novel peptide derivatives required synthetic development using both solution and solid phase techniques. The solid phase synthesis of several C-terminal 1aminoethyltetrazole peptides was successfully established by using 2-chlorotrityl chloride resin. The investigation of the antimicrobial activity of the synthesised compounds identified several clinically applicable selective inhibitors. These compounds were shown to provide differentiation between Salmonella and Escherichia coli, or enterococci and streptococci. This work also gave a useful comparison between the different alanine bioisosteres, and showed the importance of di- and oligopeptide permease systems in order to reach sufficient bacterial activity. The microbiological activity of 1- aminoethyltetrazole peptide derivatives was studied in more detail, due to their potential in clinical applications for the diagnosis of food poisoning. In other work, also directed towards the rapid and selective detection and identification of pathogenic bacteria in a clinical environment, new chromogenic substrates were prepared. Each of these compounds contained a chromogen with a phenoxazin-3-one scaffold linked to an amino acid residue. The purpose of the amino acid is to act as a unit recognised and cleaved by specific hydrolytic bacterial enzymes. Upon liberation, electronic differences between the conjugated and free forms of the chromogen resulted in the development of distinct colour changes, which provide the basis of 4 bacterial detection and identification. Synthetic methods have been developed for the efficient and economical production of this series of substrates. After preparation, these compounds were tested against a panel of clinically relevant bacteria. The aim of these substrates was to present an alternative substrate for (N-β-alanyl)-7-amino-1-pentylphenoxazine-3-one 86a, which is applied commercially in chromID® Pseudomonas aeruginosa chromogenic medium designed for the clinical detection of P.aeruginosa. The new substrates are designed to fully explore the chemical space of phenoxazinonebased chromogenic substrates, and to decrease the colour, as substrate 86a causes significant background colour in culture media. The future application of these substrates in chromogenic media resides in their potential to advance the identification of specific pathogenic bacteria and to thus facilitate the treatment of bacterial infections.
44
Dias, Diana Patrícia Pires. "Presence of pathogenic bacteria and antimicrobial resistance in Portuguese wild ungulates." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14979.
Full textAbstract:
Mestrado em MicrobiologiaAntimicrobial resistance is as an emerging global problem in both human and veterinary medicine. In theory, wild animals are rarely exposed to antimicrobial agents and therefore low levels of AMR are to be expected. However, the growing interaction of these animals with anthropogenic activities can have a huge impact in their bacterial flora. Escherichia coli is commonly found in the intestinal tract of a wide variety of animals and humans. This intestinal bacterium can be easily disseminated in different ecosystems. Therefore, it can be an useful indicator of the selective pressure exerted by the use of antimicrobials. Salmonella is a pathogenic bacterium, commonly found in the intestine of healthy birds and mammals that can cause salmonellosis in humans. In the European Union, over 90,000 salmonellosis cases are reported every year to EFSA. This study was conducted in wild ungulates from three distinct geographical areas in Portugal (Montesinho, Idanha-a-Nova and Lousã) and aimed to: i) access the levels of antibacterial resistance occurring in E. coli strains ii) determine the occurrence levels of Salmonella spp. and iii) determine the occurrence levels of shiga toxin-producing E. coli (STEC). To that purpose, a total of 67 faecal samples from red deer (n=41), wild boar (n=21) and roe deer (n=4) were collected. Before antibacterial susceptibility testing (according to the EUCAST guidelines), the E. coli isolates obtained were typed by BOX-PCR to select for genetically different strains for each sample (n=152). The detection of Salmonella was performed according to ISO 6579:2002 Annex D. Results revealed that in E. coli resistance was observed to ampicillin (10%), tetracycline (9%), streptomycin (5%), co-trimoxazole (4%), amoxicillin/clavulanic acid (2%) and cefoxitin (1%). A total of 3.3% of the isolates exhibited a multiresistant phenotype, all from Lousã. The results were also analyzed according to ECOFFs. Non-wildtype phenotypes were obtained to ampicillin (10%), ceftazidime (6%), co-trimoxazole (4%), amoxicillin/clavulanic acid (2%), aztreonam (1%) and cefotxitin (1%). A low incidence of Salmonella spp. (1.5%) was observed and it was only identified in wild boar from Lousã. The isolate was susceptible to all the tested antimicrobials. Regarding the presence of STEC, it was possible to establish that red and roe deer from the three sampling sites carry this bacterium. The stx variants detected in the STEC isolates included stx1c, stx2d and stx2g. Moreover, the hemolysin gene ehxA was identified in a strain possessing the stx2g variant. Overall, our results reveal that these populations of wild ungulates are reservoirs of antibiotic resistant and potential pathogenic bacteria. Therefore, these animals can act as dissemination vehicles between wildlife-livestock-human interfaces.
A resistência antimicrobiana é um problema emergente e global, tanto a nível clínico como veterinário. Em teoria, os animais selvagens raramente estão expostos a agentes antimicrobianos, e deste modo espera-se que a sua flora bacteriana apresente baixos níveis de resistência. Contudo, a crescente interação destes animais com atividades antropogénicas pode influenciar a aquisição de uma flora bacteriana resistente. Escherichia coli faz parte do trato intestinal de uma grande variedade de animais, incluindo o Homem. Esta bactéria pode disseminar-se facilmente em diferentes ecossistemas, sendo também um importante indicador da pressão seletiva exercida pela utilização de antimicrobianos. Salmonella spp. é uma bactéria patogénica, normalmente encontrada no intestino de diversos animais. Anualmente, na União Europeia são reportados à EFSA mais de 90,000 casos de salmoneloses. O presente estudo foi realizado em três espécies de ungulados selvagens que habitam três localizações geográficas distintas em Portugal (Montesinho, Idanha-a-Nova e Lousã) e teve como objetivos: i) avaliar os níveis de resistência de isolados de E. coli ii) determinar o nível de ocorrência de Salmonella spp. e iii) determinar o nível de ocorrência de E. coli produtora da toxina shiga (STEC). Para tal foram recolhidas 67 amostras fecais de veado (n=41), javali (n=21) e corço (n=4). Numa primeira fase os isolados recolhidos foram tipados por BOX-PCR para selecionar estirpes geneticamente diferentes em cada amostra (n=152). Posteriormente realizou-se o teste de suscetibilidade a antimicrobianos (de acordo com o EUCAST). A deteção de Salmonella foi realizada de acordo com a norma ISO 6579:2002 Anexo D. Os resultados obtidos revelaram que para E. coli se verificou resistência aos antibióticos ampicilina (10%), tetraciclina (9%), streptomicina (5%), cotrimoxazol (4%), amoxicilina/ácido clavulânico (2%) e cofoxitina (1%). Um fenótipo de multirresistência foi encontrado em 3.3% dos isolados, todos provenientes da região da Lousã. Os resultados foram também analisados de acordo com os valores de ECOFFs, tendo sido encontrados fenótipos do tipo não-selvagem para a ampicilina (10%), ceftazidima (6%), cotrimoxazol (4%), amoxicilina/ácido clavulânico (2%), aztreonam (1%) e cefoxitina (1%). No que se refere à pesquisa de Salmonella, os resultados revelaram uma baixa incidência na população estudada (1.5%). Esta estirpe revelou-se suscetível a todos os antimicrobianos testados. Relativamente à presença de STEC, foi possível determinar que veados e corços dos três locais estudados são portadores deste tipo de estirpes. Detetaram-se três variantes do gene stx nos isolados STEC, incluindo stx1c, stx2d e stx2g. Foi ainda identificado o gene ehxA, que codifica para uma hemolisina, num isolado contendo a variante stx2g. No seu conjunto, os resultados obtidos mostram que as populações de ungulados selvagens estudados são reservatórios de bactérias resistentes, assim como de bactérias potencialmente patogénicas e podem, por isso, atuar como veículo de transmissão entre a vida selvagem, o gado e o Homem.
45
Mody, Shreena Himanshu. "The Antimicrobial Properties of Honey and Their Effect on Pathogenic Bacteria." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7042.
Full textAbstract:
Honey has been used to heal wounds since ancient times. There are many references in ancient literature that cite honey for its medicinal uses. It is used as an alternative agent to cure infections of wounds, burns, ulcers etc. Researchers have shown some of the antimicrobial properties of honey when used as an ointment. When applied to an affected area, it helps to promote the growth of healthy tissue. One of the factors on which the quality of the honey depends, is its geographical origin. Based on the location, honey types can vary as much as 100-fold from each other in color, aroma, viscosity, and antimicrobial properties. The important components in honey that play an essential part in healing wounds and contributing to the antimicrobial properties are enzymes. Their presence allows honey to kill various types of pathogenic bacteria, viruses, fungi etc. A higher antimicrobial effect is seen in monofloral honey (when a single plant species is the source of nectar), which is often more potent than other types of honey in terms of antibacterial activity. Resistance of pathogens to these antimicrobial actions has never been shown, which makes honey a more promising source of antimicrobial research. Presently, infections of burns and wounds are very challenging to treat, especially when they are caused by antibiotic-resistant bacteria. The purpose of this study was to examine the antimicrobial properties of honey from Utah and other locales, and to identify promising antimicrobial activities that could be useful in treating infections caused by resistant bacteria.
46
Ryzhkova, T. A., E. M. Babych, S. V. Kalinichenko, and N. I. Sklyar. "Antagonistic activity of lactobacillus strains against pathogenic corynebacteria in different cultivation conditions." Thesis, Сумський державний університет, 2013. http://essuir.sumdu.edu.ua/handle/123456789/32129.
Full textAbstract:
The most abundantly used probiotic strains come from the genus Lactobacillus. It is well known that probiotics can improve patient condition in medical disorders such as diarrhoea, gastroenteritis, short-bowel syndrome, and inflammatory intestinal diseases (Crohn’s disease and ulcerative colitis) and only a few studies have investigated their role in oral health.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/32129
47
Subires, Orenes Alicia. "Optimization of flow cytometry assays for the detection of injured foodborne pathogenic bacteria." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/311611.
Full textAbstract:
Algunos tratamientos de elaboración y conservación de los alimentos lesionan las bacterias, de manera que pierden la capacidad para multiplicarse y no son detectadas por métodos de cultivo convencionales. La citometría de flujo es una técnica de análisis independiente del cultivo de los microorganismos, usada ampliamente para evaluar de manera rápida el estado fisiológico de células bacterianas individuales, siendo la integridad de membrana unos de los indicadores más habituales debido a su importancia en la supervivencia de éstas. Sin embargo, los resultados obtenidos mediante citometría de flujo se ven afectados por la presencia de partículas de las muestras alimentarias.
En esta tesis, se evaluaron estrategias para desarrollar un ensayo por citometría de flujo basado en el uso del yoduro de propidio (YP), fluorocromo que no atraviesa las membranas intactas, combinado con un fluorocromo que penetra las membranas intactas, para detectar y cuantificar con precisión bacterias patógenas lesionadas. En el primer experimento, se ajustaron las concentraciones y las ratios de combinaciones de YP con SYTO 9, SYTO 24 y SYTO BC para mejorar la resolución de poblaciones de células sanas y muertas de Escherichia coli O157:H7, Salmonella Enteritidis y Listeria monocytogenes en suspensiones control. Esto permitió detectar células lesionadas en suspensiones expuestas a estreses relacionados con los alimentos. En el segundo experimento, se aplicaron las tinciones optimizadas a muestras de ensalada de pasta inoculadas con E. coli O157:H7. Asimismo, se compararon ocho pre-tratamientos basados en la filtración gruesa de las muestras homogeneizadas y en un paso de dilución/lavado, para evaluar la reducción de partículas interferentes y la recuperación de E. coli O157:H7 de la ensalada. El pre-tratamiento más favorable fue la combinación de la bolsa de homogenización con filtro de 63 µm y la filtración centrífuga a través de un filtro de 5 µm, ya que redujo la concentración de partículas interferentes tanto como diluir la muestra. Considerando que el objetivo principal de esta tesis fue detectar específicamente bacterias patógenas lesionadas, en el tercer experimento, la optimización se llevó a cabo para suspensiones control de E. coli O157:H7 en soluciones tampón comúnmente usadas en inmunoensayos, y teñidas con SYBR Green I, un fluorocromo con alta afinidad por los ácidos nucleicos, YP y un anticuerpo marcado con R-ficoeritrina (Ac-RFE). La adición de Ac-RFE no afectó notablemente la resolución de las poblaciones en comparación con la resolución conseguida con la tinción con SYBR Green I y YP, y permitió reconocer claramente las células de E. coli O157:H7. En el cuarto experimento, se evaluaron estrategias de filtración de señal analítica para reducir la adquisición de datos procedentes de partículas interferentes. Posteriormente, se aplicó el pre-tratamiento de muestra optimizado, la tinción para evaluar la integridad de membrana y la inmunodetección, y la filtración de señal analítica, para monitorizar los cambios de la integridad de membrana de E. coli O157:H7 inoculada en ensalada de pasta durante 14 días de almacenamiento en refrigeración (pH 4,5; 4°C). Con este protocolo optimizado, el límite de detección disminuyó a 5 log UFC/g. Además, se observó que la mayoría de células de E. coli O157:H7 estaban lesionadas al principio del almacenamiento, pero mostraban una membrana intacta al final, lo que sugiere que las células lesionadas repararon su membrana durante la exposición a ácido y refrigeración y, por lo tanto, sobrevivieron en la ensalada de pasta.
En conclusión, el ensayo por citometría de flujo para la evaluación de la integridad de membrana y la inmunodetección desarrollado en esta tesis es una buena herramienta para monitorizar el efecto de tratamientos relacionados con los alimentos sobre el estado de la membrana de E. coli O157:H7, parámetro fisiológico relacionado con la presencia de células lesionadas.Nowadays, one of the key factors driving consumer food choice is convenience. This has led to an increase in the ready-to-eat (RTE) meal market, with a consequent emergence of new food safety hazards, since food processing and preservation technologies that may be applied to these food products have a milder effect on microorganisms than traditional food processing strategies (e.g. pasteurization, sterilization). As a result, some of those technologies render injured bacteria, which may lose their ability to multiply and are therefore not detected by conventional plating. However, their presence in food must not be overlooked, due to their potential capacity to recover and pose a hazard to health in the case of pathogens. Flow cytometry is a culture-independent technique which has been widely used in bacterial research to rapidly assess the physiological state of individual cells, with membrane integrity being one of the most popular parameters due to its essential role in survival. However, flow cytometry results are largely affected by the interference of food particles. In this thesis, several strategies were evaluated to develop a flow cytometry assay, based on the use of the membrane-impermeant dye propidium iodide (PI) combined with a membrane-permeant dye, to accurately detect and enumerate injured pathogenic bacteria. In the first experiment, concentrations and ratios of combinations of PI with SYTO 9, SYTO 24, and SYTO BC were adjusted to improve resolution of healthy and dead Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes populations in control suspensions. This allowed detection of injured cells in suspensions exposed to food-related stresses. In the second experiment, optimized stainings were applied to RTE pasta salad samples inoculated with E. coli O157:H7. Moreover, eight different salad sample pre-treatments based on coarse filtration of homogenates and a dilution/wash step were compared in terms of background particle reduction and E. coli O157:H7 recovery. The most advantageous pre-treatment was the combination of a 63-µm filter blender bag and centrifugal filtration through a 5-µm filter, since it was equivalent to sample dilution in reducing background particle concentration. Considering that the ultimate goal of this thesis was to detect specific injured pathogen cells in RTE pasta salad, in the third experiment, optimization was carried out for E. coli O157:H7 control suspensions in buffers commonly used in immunoassays and stained with the high-affinity nucleic acid dye SYBR Green I, PI, and an R-phycoerythrin-labeled antibody (Ab-RPE). Addition of Ab-RPE did not remarkably affect population resolution compared with staining only with SYBR Green I and PI, and allowed clear recognition of E. coli O157:H7. Finally, in the fourth experiment, a range of signal filtering strategies were evaluated for reduced acquisition of flow cytometry data arising from interfering food particles. Then, optimized salad sample pre-treatment, combined membrane integrity and immunodetection staining, and signal filtering were applied to monitor the changes in membrane integrity of E. coli O157:H7 inoculated in pasta salad throughout 14-day refrigerated storage (pH 4.5, 4°C). With this optimized flow cytometry protocol, the limit of detection of the assay was reduced to 5 log CFU/g. Additionally, it was observed that most E. coli O157:H7 cells were injured at the beginning of refrigeration, but showed an intact membrane at the end, which suggests that injured cells repaired their membrane during exposure to refrigeration and acid stresses, and therefore survived in RTE pasta salad. In conclusion, the immunodetection and membrane integrity flow cytometry assay in food samples developed in this thesis is a good tool to monitor the effect of a number of food-related treatments on E. coli O157:H7 cell membrane state, a physiological parameter that can be related to the presence of injured cells.
48
Doherty, Alice Majella. "Growth of a number of pathogenic bacteria on modified atmosphere packaged lamb." Thesis, University of Ulster, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339314.
Full text
49
Pfeilmeier, Sebastian. "Elicitation and evasion of plant innate immunity by beneficial and pathogenic bacteria." Thesis, University of East Anglia, 2017. https://ueaeprints.uea.ac.uk/66876/.
Full textAbstract:
Plasma membrane-localized pattern recognition receptors (PRRs) are central components of the plant innate immune system. PRRs perceive characteristic microbial features, termed pathogen-associated molecular patterns (PAMPs), leading to pattern-triggered immunity (PTI). As PAMPs from both pathogenic and beneficial bacteria are potentially recognized, both must employ strategies to evade and/or suppress PTI. Here, I show that exopolysaccharides (EPS) and flagella-driven motility, both of which are regulated by the secondary messenger cyclic-di-GMP, are important virulence factors at different stages during Pseudomonas syringae pv. tomato (Pto) DC3000 infection of Arabidopsis thaliana. High levels of cyclic-di-GMP impaired flagellin accumulation in different Pseudomonas species, and helped bacteria to evade recognition by the PRR FLAGELLIN SENSING 2. In this case, immune evasion was fully explained by the effect of cyclic-di-GMP on flagellin synthesis rather than on EPS production. Nevertheless, an EPS-deficient Pto DC3000 mutant, Δalg/psl/wss, showed compromised virulence, and a combination of two types of EPS appeared to be required for optimal in planta proliferation. In a complementary project, I tested whether PAMP recognition affects the interaction between the legume Medicago truncatula and its symbiotic partner Sinorhizobium meliloti. I transferred the PRR EF-TU RECEPTOR (EFR) from A. thaliana to M. truncatula, conferring recognition of the bacterial EF-Tu protein. Expression of EFR protected M. truncatula against the root pathogen Ralstonia solanacearum without compromising the overall symbiotic interaction with nitrogen-fixing S. meliloti. My results indicate that rhizobium either avoids PAMP recognition, or actively suppresses immune signalling during the infection process. Finally, I engineered a PAMP in S. meliloti by replacing the eliciting inactive flg22 epitope (derived from flagellin) with an eliciting epitope. My results suggest that legumes can be engineered with novel PRRs, as a biotechnological approach for broad-spectrum disease resistance, without perturbing the nitrogen-fixing symbiosis. Overall, my work contributes to our understanding of the molecular interaction between plants and bacteria.
50
Pereira, Carla Sofia Gomes. "Use of bacteriophages on the inactivation of pathogenic bacteria in aquaculture system." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/4511.
Full textAbstract:
Mestrado em MicrobiologiaA importância crescente da aquacultura a nível mundial contribui para compensar a progressiva redução das populações naturais de peixe. Contudo, o facto de várias pisciculturas sofrerem, frequentemente, grandes perdas económicas, devido a infecções causadas por microrganismos patogénicos, incluindo bactérias multiresistentes, torna urgente o desenvolvimento de estratégias menos lesivas para o ambiente. A Terapia fágica surge como uma potencial e emergente alternativa ao uso de antibióticos e outros antimicrobianos. O principal objectivo deste trabalho consistiu na avaliação da eficácia da terapia fágica para inactivar bactérias patogénicas de peixes em pisciculturas de regime semi-intensivo, sendo que para isso foram efectuados diversos estudos prévios. A dinâmica sazonal das comunidades virais e bacterianas foi seguida em amostras de água da piscicultura Corte das Freiras, tendo-se identificando as principais bactérias patogénicas e avaliado o nível de contaminação fecal. O número total de vírus foi determinado por microscopia de epifluorescência e a abundância relativa das principais bactérias patogénicas determinada por FISH (Fluorescent in situ hibridization). A dinâmica sazonal da comunidade bacteriana foi avaliada por 16S rDNA DGGE (Denaturing Gradient Gel Electrophoresis). Uma vez que vibriosis e photobacteriosis representam duas das principais causas de mortalidade nos peixes em pisciculturas, a diversidade da comunidade bacteriana do género Vibrio também foi avaliada por DGGE. O nível de contaminação fecal foi avaliado através da quantificação do teor de coliformes fecais e de enterococos fecais, usando o método das membranas de filtração. Para o estudo da cinética da interacção bactériabacteriófago usou-se a infecção cruzada. Para aplicar com sucesso a terapia fágica é importante ter informações sobre a sobrevivência dos fagos e o seu impacto ecológico na estrutura da comunidade bacteriana após adição dos fagos das principais bactérias patogénicas de peixe. Os resultados obtidos mostram que o número total de vírus na água da aquacultura é bastante elevado, variando entre 6.1 x 109 particulas L-1 e 1.0 x1010 particulas L-1. O número total de bactérias permanece praticamente constante, contudo os grupos específicos de bactérias variam significativamente ao longo dos períodos de amostragem. No caso dos indicadores bacterianos, foi observada uma clara variação sazonal, com os níveis mais elevados de poluição fecal registados em Outubro de 2007 e os mais baixos registados em Maio 2009. A análise de fragmentos de 16S rDNA por DGGE sugere que a estrutura da comunidade bacteriana varia sazonalmente, verificado-se uma maior diversidade na estação mais quente. No caso do género Vibrio a análise por DGGE sugere também uma variação sazonal na comunidade bacteriana pertencente a este género, ainda que não tão evidente. Os resultados de infecção cruzada sugerem que, com excepção do fago de Aeromonas salmonicida , os fagos inoculados nas principais bactérias patogénicas de peixe apresentam um largo espectro de infecção do hospedeiro. A sobrevivência dos fagos na água da aquacultura variou, sendo que o fago de Aeromonas salmonicida sobreviveu aproximadamente 3 meses, enquanto o fago de Vibrio parahaemolyticus sobreviveu cerca de 15 dias. A adição dos fagos à comunidade bacteriana não conduziu a uma variação significativa na estrutura da comunidade bacteriana. Em conclusão, como o teor de vírus e a sobrevivência dos fagos na água da aquacultura são elevados e a adição dos fagos específicos das bactérias patogénicos tem um baixo impacto ecológico na estrutura da comunidade bacteriana natural, a terapia fágica pode ser aplicada com sucesso na inactivação das bactérias patogénicas de peixes. Além disso, a infecção múltipla pelos fagos aumenta a capacidade de inactivação de bactérias patogénicas. No entanto, como a densidade e a estrutura das comunidades bacterianas totais e patogénicas varia sazonalmente, torna-se necessário ter este facto em consideração aquando da escolha dos fagos a utilizar para terapia fágica.
Due to the increasing importance of aquaculture for the compensation of progressive worldwide reductions in natural fish stocks and to the fact that several fish farming plants often suffer from heavy financial losses due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, more environmentally-friendly strategies to control fish infections are urgently needed to make the aquaculture industry more sustainable. Phage therapy is an emerging and potential viable alternative to antibiotics and other antimicrobials. The main target of this work was to evaluate the use of phage therapy to inactive fish pathogenic bacteria in aquaculture systems, thus, several preliminary studies were developed. In this work the seasonal dynamics of viral and bacterial communities of the aquaculture system Corte das Freiras was followed, the main pathogenic bacteria were identified and the level of faecal contamination in the aquaculture was evaluated. The total number of viruses was determined by epifluorescence microscopy and the relative abundance of specific bacterial groups of was accessed by FISH (Fluorescent In Situ Hybridization). The seasonal dynamics of bacterial community structure was evaluated using 16S rDNA DGGE (Denaturing Gradient Gel Electrophoresis). As vibriosis and photobacteriosis represent two of the main causes of fish mortality in fish farms, the diversity of the fish pathogens belonging to the Vibrio genus was also assessed by DGGE. The level of faecal contamination was evaluated through the quantification of faecal coliforms and faecal enterococci, using the membrane filtration method. The kinetics of pathogenic bacteria-phages interaction was also studied in laboratory, using cross infection. In order to apply phage therapy successfully, it is important to know the survival of the phage and the ecological impact of phage therapy in the diversity of bacterial communities after the additions of phages of the main fish pathogenic bacteria. The results obtained show that the number of viruses in the aquaculture water was high, varying between 6.1 x 109 cells L-1 and 1.0 x1010 cell L-1. The number total bacteria was almost constant over the year, but the specific bacterial groups varied significantly during the sampling period.A clear seasonal variation in bacterial indicators was observed, with the highest values of faecal bacteria occurring in October 2007 and the lowest in May 2009. The 16S rDNA DGGE results showed that bacterial community structure varied seasonally, showing a higher diversity during the warm season. The diversity of the Vibrio genus also showed a seasonal variation, but not so clear. The cross infection results showed that, with the exception of Aeromonas salmonicida phage, the phages inoculated on the main fish pathogenic bacteria displayed a large spectrum of host infection. The survival of the phages was variable; the Aeromonas salmonicida phage survived in aquaculture water during approximatelly three months and the phage of Vibrio parahaemolyticus survived only during fifteen days. Phage addition to the bacterial community did not result in a significant variation in bacterial community structure. In conclusion, as the level of viruses and survival of these phages are high in water from the aquaculture system and the addition of specific phages of pathogenic bacteria has a low ecological impact on the structure of the natural bacterial community, suggests that phage therapy can be a successful approach to inactivate fish pathogenic bacteria. Moreover, the occurrence of multiple infections by these phages improve their potential to inactive fish pathogenic bacteria. However, as the density and structure of total and pathogenic bacterial communities varied seasonally, it is necessary to take in consideration this variation when specific phages are selected for phage therapy.