Tesi sul tema "Virulence determinant"
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1
Aish, Joanne Louise. "Environmental regulation of virulence determinant expression in Staphylococcus aureus". Thesis, University of Sheffield, 2003. http://etheses.whiterose.ac.uk/3030/.
Abstract (sommario):
Staphylococcus aureus is a highly versatile pathogen that causes a wide range of diseases. Appropriate gene expression in various niches within the human body and abiotic environments requires the sensing of environmental conditions. An important environmental parameter affecting S. aureus is NaC1 concentration. This study investigated S. aureus virulence determinant regulation in the presence and absence of NaCl stress. In the absence of NaCl stress, aB was found to repress hla transcription and protease activity, possibly via the repression of agr transcription. The effect of aB on agr probably occurs indirectly, although sarA, sarHi and rot are unlikely to function as intermediates in this pathway. Tn551 mutagenesis identified numerous genes, including lysC, ykuQ, lysA, brnQ and telA, which repress hla transcription and protease activity by upregulating aB activity. These genes are clustered in the SVS (S. aureus virulence and survival) region of the S. aureus genome, in which transposon insertion affected the virulence and survival of mutants isolated in numerous published screens. Other SVS region genes, including asd, dapA, hipO, ac1P and norQ were also found to repress hla transcription and protease activity by upregulating aB activity. In the presence of NaCl stress, virulence determinants (which are normally regulated by agr) come under the control of a novel regulatory system involving an-dependent and aB-independent pathways. Tn917 mutagenesis identified several genes, including citG, opuD, yugT, oppF, ykrP, eprH, yubA, unkl and unk2, which have putative roles in the aB-independent pathway. The SVS region genes analysed may function in the aB- dependent pathway. The sensor saeS was found to upregulate hla transcription in the absence of NaCI stress and may be involved in sensing NaCI stress. The NaCI stress signal may act in concert with other parameters to allow stringent virulence determinant regulation in response to the prevailing environmental conditions.
2
Horsburgh, Samantha. "Identification of novel regulators of virulence determinant production in Staphylcoccus aureus". Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274960.
3
Dade, Jessica E. "HcZrt2, a Zinc Transporter and Nutritional Virulence Determinant in Histoplasma Capsulatum". University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470753451.
4
Apagyi, Katinka. "Characterization of a novel virulence determinant in Erwinia carotovora subspecies atroseptica SCRI1043". Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/265545.
Abstract (sommario):
This study focused on the characterization of the gene rsmS in Erwinia carotovora subsp. atroseptica (Eca). Eca is a phytopathogenic Gram-negative bacteria, producing virulence factors, such as plant cell wall degrading enzymes {PCWDEs), which enable the initiation and maintenance of host plant invasion. rsmS was shown to encode a short polypeptide, and it has orthologues in many Gramnegative agriculturally and medically relevant bacteria. Plate and spectrophotometry-based assays and microarray studies showed that RsmS suppressed the transcription and activity of several PCWDEs, the transcription of type one, two and six secretion systems and of some of their substrates. RsmS also suppressed general virulence exhibited by Eca in potato tubers, and on the quorum sensing signaling molecule N-{3-oxohexanoylh-homoserine lactone. In many ways, RsmS acted in a similar fashion to RsmA, r a well characterized suppressor of virulence determinants (such as PCWDEs) and quorum sensing found in a wide variety of Gram-negative bacteria. RsmA activated rsmS transcription, and the transcription of both rsmS and rsmA was shown to be upregulated with increasing temperature. Thus, it is possible that RsmA exerts some of its inhibitory effects on virulence determinants through the positive regulation of RsmS. rsmS was shown to be transcribed from a promoter shared with its upstream neighbour, priC. It may also be transcribed from a promoter located within the priC open reading frame, but this result remains to be confirmed with future experiments. Although the genomic arrangement of priC and rsmS is conserved in almost all bacteria with an rsmS orthologue, no further regulatory connection was shown between their protein products. Interestingly, when rsmS was overexpressed without a 225 bp region located within priC, PCWDE activity was increased, in all mutant strains of Eca tested. The reason behind this dominant negative phenotype remains to be fully elucidated by future experiments. Both microarray and plasposon mutagenesis studies identified several genes coding for factors that are regulated by, or regulate, RsmS. It will require further analysis and experiments to unveil which one of these actually interacts with RsmS (directly or indirectly). Such genes include CRISPR-like genes, members of nitrogen metabolism pathways and membrane transport.
5
Mateo, Montalcini Solange A. "AGC kinase Sta1 is a virulence determinant in the rice blast fungus". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531838.
6
Stapleton, Melanie. "Studies with SlyA, a transcription regulator and virulence determinant of Salmonella typhimurium". Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274957.
7
Marroquin, Stephanie Michelle. "A Novel Abi-domain Protein Controls Virulence Determinant Production in Staphylococcus aureus". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6725.
Abstract (sommario):
A major factor in the success of Staphylococcus aureus as a pathogen is its vast arsenal of virulence determinants and, more importantly, the tight and precisely- timed regulation of these factors. Here we investigate the product of the S. aureus gene, SAUSA300_1984, encoding a putative transmembrane protein. This as yet uncharacterized protein belongs to the Abi (abortive infection) family, which are commonly annotated as CAAX-proteases, and are significantly understudied in prokaryotes. In S. aureus the disruption of SAUSA300_1984 results in a drastic reduction of proteolytic and hemolytic activity, as well as diminished pigmentation. This phenotype appears to be mediated through reduced agr expression, as determined by qPCR analysis. Importantly, known regulators of agr, such as CodY, MgrA, and ArlR, demonstrate no significant changes in transcription upon 1984 disruption, whilst major alterations were observed for downstream effectors of agr, such as sarS, RNAIII, rot and hla. Complementation and site-directed mutagenesis of 1984 demonstrated that proteolytic activity (via conserved EE residues) was not required for this phenotype, suggesting a potential protein-protein interaction mechanism of interaction. Proteome analysis of the 1984 mutant confirmed a number of our transcriptional observations, such as an increased abundance of Rot and surface associated proteins, as well as a marked decrease in Agr-system proteins levels, with the most striking being AgrB. Virulence profiling revealed a decreased ability of the 1984 mutant to evade constituents of the innate immune response, and impaired survival during murine models of infection. Given that SAUSA300_1984 is encoded 3 genes downstream of RNAIII, our current working hypothesis is that this Abi protein functions to control agr activity through communication with membrane components of this system, potentially via interaction with AgrB. Confirming this, and determining the upstream effectors of this regulatory system are studies currently ongoing in our laboratory.
8
Price, Maeve. "SSWl encodes a glycolipid-anchored surface protein and is a virulence determinant in M oryzae". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526103.
9
Sodeinde, Olanrewaju A. "Identification and Characterization of the Virulence Determinant of the 9.5 Kilobase Plasmid of Yersinia Pestis: a Thesis". eScholarship@UMMS, 1990. http://escholarship.umassmed.edu/gsbs_diss/310.
Abstract (sommario):
The pathogenicity of Yersinia pestis, the causative agent of plague, is specified by chromosomal and plasmid encoded genes. At least two plasmids, with sizes of 9.5 and 75 kilobases, are indispensable to the full expression of virulence. Loss of the 75 kb plasmid results in outright avirulence. Strains lacking the 9.5 kb plasmid exhibit LD50s at least six orders of magnitude greater than wild-type following subcutaneous or intraperitoneal infection of mice or guinea-pigs but have LD50s as low as wild-type when injected intravenously. Four biochemical properties are associated with the 9.5 kb plasmid. These include plasminogen activator and coagulase activities in addition to the bacteriocin pesticin, and its immunity determinant. A genetic analysis of this plasmid was undertaken as a first step towards the identification and characterization of its virulence determinant(s). This led to the construction of a physical and genetic map of the plasmid. Four loci were mapped to the plasmid: pst and pim, which encode pesticin and its immunity determinant respectively; pla, which encodes both plasminogen activator and coagulase activities; and ori/inc, the locus containing both the origin of replication and the region responsible for the control of plasmid incompatibility. pst was shown to encode a 45 kD protein but the pim gene product was not identified. pla encodes two outer membrane proteins, α- and β-Pla of 37 and 35 kD, respectively, the latter being derived from the former most probably by a proteolytic processing event. At least one of these proteins is responsible for the highly specific degradation of the YOPs, a set of virulence-associated outer membrane proteins encoded by the 75 kb plasmid. The nucleotide sequence of pla revealed that it possessed significant homology to both prtA (geneE) of Salmonella typhimurium and ompT of Escherichia coli. Subcutaneous infection of mice with isogenic strains of Y. pestis harboring well defined mutations in the genes that reside on the 9.5 kb plasmid revealed that pla is a virulence determinant of Y. pestis, and also that of the genes harbored by the plasmid, pla is both necessary and sufficient to account for the high degree of virulence of Y. pestis for mice from subcutaneous sites of infection. pla encodes an activator of human, rat, and mouse plasminogen but does not induce coagulation of plasma obtained from these species. Treatment of mice with the antifibrinolytic agent, trans-4(aminomethyl)-cyclohexanecarboxylic acid did not affect the outcome of plague infection, indicating that fibrinolysis per se does not play a role in plague pathogenesis.
10
Kleij, Lena. "Identification and validation of the virulence determinants of circulating equine influenza viruses". Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASL136.
Abstract (sommario):
Les virus influenza sont des virus enveloppés, à ARN négatif segmenté en 8 segments génomiques. Ils sont classés dans la famille des Orthomyxoviridae. Ce sont les agents étiologiques de la grippe, une maladie respiratoire qui touche de nombreuses espèces mammifères et aviaires. La grippe équine est causée par les sous-types H3N8 et H7N7 du virus influenza de type A, ce dernier s'étant éteint depuis les années 1970. Malgré l'existence d'un vaccin, la France a connu plusieurs épidémies de H3N8 depuis les années 2000. Pour réduire l'impact économique important de ces épidémies pour l'industrie équine, il est nécessaire d'établir des tests de diagnostic rapides, robustes et applicables sur le terrain pour limiter au plus la circulation du virus et en identifier les déterminants de virulence et caractériser la dérive antigénique.Nous avons étudié les potentialités de la technique de séquençage dite « long read » développée par Oxford Nanopore Technologies. Nous avons réalisé une caractérisation du génome complet de deux virus H3N8 équins ayant circulé en France en 2009 et 2018 (A/équine/Paris/1/2018 et A/équine/Beuvron-en-Auge/2/2009, deux virus de la clade 1 Florida) ainsi que des deux souches du vaccin couramment utilisé en France.Nos résultats ont démontré la fiabilité de cette technique de séquençage à partir d'amplicons des huit segments génomiques des quatre virus analysés ainsi que la capacité à réaliser des lectures fiables à partir du séquençage direct des ARN viraux (résultats présentés dans une première partie). L'analyse de la séquence en acides aminés de l'hémagglutinine HA des souches circulantes ont mis en évidence une très légère dérive antigénique par rapport aux souches vaccinales avec des substitutions spécifiques comme T161I dans A/equine/Paris/1/2018 and N188T dans les souches post-2015, deux substitutions localisées dans le site antigénique B. Le site antigénique E montre également des modifications dans les souches post-2018, avec la substitution N63D.Le segment génomique 2 code pour une des trois sous-unités de l'ARN-polymérase virale, PB1 ainsi que pour une protéine accessoire, PB1-F2, d'un cadre de lecture alternatif. PB1-F2 est reconnu comme un déterminant de virulence. Alors que la souche A/équine/Paris/1/2018 code pour un variant de 90 acides aminés de long, de nombreuses souches, dont A/équine/Beuvron-en-Auge/2/2009, code pour un variant de seulement 81 résidus. Des essais biologiques et de biochimie ont été réalisés pour caractériser les propriétés de chacune de ces deux formes de PB1-F2. Dans un essai où la forme longue de PB1-F2 est exprimée en cellules eucaryotes sans autre constituant viraux, elle abolit le potentiel membranaire de la mitochondrie cellulaire. Mise en présence de vésicules synthétiques mimant la membrane externe de la mitochondrie, la forme longue de PB1-F2 les perméabilise plus efficacement que la forme courte. Les analyses de séquence en acides aminés des protéines virales (de HA et PB1-F2 essentiellement) sont présentées dans une deuxième partie.Afin de valider l'impact de PB1-F2 sur la virulence en contexte infection, nous avons cherché à établir un système de génétique inverse pour le virus A/équine/Paris/1/2018 (troisième partie). Pour se faire, les 8 segments génomiques ont été clonés dans le plasmide pRF483 permettant d'assurer la synthèse des brins d'ARN génomiques et l'expression des protéines virales. La séquence des inserts de chacun des plasmides a été validée. Pour valider le fonctionnement du complexe réplicatif codé par 4 des 8 segments viraux clonés dans pRF483 (PA, PB1, PB2 et NP), ces plasmides ont été transfectés avec un plasmide codant pour le segment génomique NA dans lequel son cadre de lecture a été substitué par un gène reporter, la luciférase. Dans ces conditions expérimentales, une activité du complexe ARN-polymérase a été détectée. Ces essais seront prolongés pour la production de virus recombinants par transfection des 8 plasmides construitsInfluenza viruses are enveloped, their genome being segmented into 8 negative RNA segments. They are classified in the Orthomyxoviridae family. They are the etiological agents of the flu, a respiratory disease that affects many mammalian and avian species. Equine influenza is caused by the H3N8 and H7N7 subtypes of the type A influenza virus, the latter being extinct since the 1970s. Despite the existence of a vaccine, France has experienced several H3N8 epidemics since the 2000s. To reduce the significant economic impact of these epidemics for the equine industry, it is necessary to establish rapid, robust, and on-terrain applicable diagnostic tests to limit the circulation of the virus as much as possible and identify its virulence determinants as well as characterize antigenic drift.We studied the potential of the so-called “long read” sequencing technique developed by Oxford Nanopore Technologies. We carried out a characterization of the complete genome of two equine H3N8 viruses that circulated in France in 2009 and 2018 (A/equine/Paris/1/2018 and A/equine/Beuvron-en-Auge/2/2009, two viruses of clade 1 Florida) as well as the two strains of the vaccine commonly used in France.Our results demonstrated the reliability of this sequencing technique using amplicons of the eight genomic segments of the four viruses analyzed as well as the ability to produce reliable readings from direct sequencing of viral RNA (results presented in the first part). Analysis of the amino acid sequence of hemagglutinin HA of circulating strains demonstrated a very slight antigenic drift compared to vaccine strains with specific substitutions such as T161I in A/equine/Paris/1/2018 and N188T in the post-2015 strains, two substitutions located in the antigenic site B. The antigenic site E also shows modifications in the post-2018 strains, with the N63D substitution.Genomic segment 2 encodes one of the three subunits of the viral RNA polymerase, PB1, as well as an accessory protein, PB1-F2, of an alternative reading frame. PB1-F2 is recognized as a virulence determinant. While the A/equine/Paris/1/2018 strain encodes a variant 90 amino acids long, many strains, including A/equine/Beuvron-en-Auge/2/2009, encode a variant only 81 residues. Biological and biochemical tests were carried out to characterize the properties of each of these two forms of PB1-F2. In an assay where the long form of PB1-F2 is expressed in eukaryotic cells without other viral constituents, it abolishes the membrane potential of the cellular mitochondria. Placed in the presence of synthetic vesicles mimicking the mitochondrial outer membrane, the long form of PB1-F2 permeabilizes them more effectively than the short form. Amino acid sequence analyzes of the viral proteins (mainly HA and PB1-F2) are presented in a second part.In order to validate the impact of PB1-F2 on virulence in an infectious context, we sought to establish a reverse genetics system for the A/equine/Paris/1/2018 virus (third part). To do this, the 8 genomic segments were cloned into the pRF483 plasmid to ensure the synthesis of genomic RNA strands and the expression of viral proteins. The sequence of the inserts of each of the plasmids was validated. To validate the functioning of the replicative complex encoded by 4 of the 8 viral segments cloned in pRF483 (PA, PB1, PB2 and NP), these plasmids were transfected with a plasmid coding for the NA genomic segment in which its reading frame was substituted. by a reporter gene, luciferase. Under these experimental conditions, activity of the RNA-polymerase complex was detected. These tests will be extended for the production of recombinant viruses by transfection of the 8 constructed plasmids
11
Borgia, Sergio M. "Characterization of a virulence determinant from group A Streptococcus, identification of a novel chromosomal region responsible for streptolysin S production in Streptococcus pyogenes". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/MQ45472.pdf.
12
Harper, Marina. "Virulence determinants of Pasteurella multocida". Monash University, Dept. of Microbiology, 2003. http://arrow.monash.edu.au/hdl/1959.1/9341.
13
Atkins, Timothy Philip. "Virulence determinants of Burkholderia pseudomallei". Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325608.
14
Kapoor, Sanjay. "Molecular determinants of rotavirus virulence". Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/4250/.
Abstract (sommario):
Rotaviruses are the single most important etiological agent of severe diarrhoea in infants and young children in both developed and developing countries. The World Health Organisation has identified the development of a rotavirus vaccine as a priority area for routine childhood immunisation to control rotavirus infections. However, the candidate vaccine strains have not been very successful. The main aim of this project was to map rotavirus virulence to its gene segments. Such studies can help in developing better vaccines for the control of rotavirus induced diarrhoea. A three step approach was undertaken (i) development of an animal model, (ii) construction and characterisation of reassortants between rotavirus strains of different virulence, (iii) mapping virulence to rotavirus gene segments. The mouse model developed revealed that the outcome of rotavirus infection was influenced by viral dose and viral strain as well as by host age and host strain. Homologous murine rotavirus strain was found to be most virulent. Among the heterologous strains studied, the OSU strain was found to be most virulent and UKtc strain the least virulent. The CD- 1 strain of mouse was found to be the most susceptible to virus infection and C57/BL the least susceptible. A very simple and rapid nucleic acid extraction method has been developed that requires only one centrifugation step and circumvents the use of any hazardous organic chemicals, which can be applied to very large numbers of samples saving time and labour. Rotavirus reassortants were constructed in a variety of ways and their genotype determined from relative mobility of their gene segments on polyacrylamide gels and restriction enzyme digestion of PCR amplified products. Twenty two reassortants (2%) were identified out of more than 1100 progeny clones examined and these reassortants belonged to 15 different genotypes. Possible reasons for obtaining this low number of reassortants are discussed. No reassortant could be identified between a murine rotavirus and other heterologous rotavirus strains. Preliminary sequence of VP7 gene of murine rotavirus strains, EDIM and EBR, was found to be different to the published rotavirus sequences including the recently published five murine rotavirus strains. The virulence mapping studies conducted in mice with some of the 22 reassortants obtained in the present study showed that gene 4 of the OSU and UKtc strains was involved in virulence. Segment 5 of OSU strain and segments 5, and 8 of UKtc strain may also be involved in virulence.
15
Tamošiūnaitė, Aistė [Verfasser]. "Cowpox virus virulence determinants / Aistė Tamošiūnaitė". Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1191180964/34.
16
Janowicz, Anna Agata. "Molecular determinants of bluetongue virus virulence". Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6959/.
Abstract (sommario):
Bluetongue virus (BTV) is an arbovirus and the cause of “bluetongue”, a major infectious disease of ruminants. Whilst the BTV structure and replication strategies are well elucidated, less is known on the genetic variability of BTV and the molecular determinants affecting virus-host interactions. In order to investigate the determinants of BTV virulence, in this study, we compared the phenotype and genotype of a highly virulent strain of BTV-8 isolated in the Netherlands a passaged minimally in tissue culture (BTV8L), with a strain passaged extensively in tissue culture (BTV8H). BTV8L was shown to be highly pathogenic in sheep and in a mouse model of bluetongue, while BTV8H was attenuated in both hosts. Full genome sequencing revealed differences in 16 amino acid residues between these two strains. Using reverse genetics, we rescued both viruses, in order two further dissect their biological features. Rescued viruses retained the phenotype of the parental viruses in vivo and in vitro. Reassortants between BTV8L and BTV8H showed that mutations in several segments contributed to attenuation of the high passage virus. The major determinants of BTV8 virulence in IFNAR-/- mice were shown to be located in segments 1, 2, 6 and 10. In vitro studies of selected reassortants showed that through extensive passage in tissue culture BTV8H acquired increased affinity for glycosaminoglycans. This property was conferred by mutations in segment 2 and resulted in increased yields of the virus in vitro and attenuation in vivo. Additionally, BTV8H was unable to replicate in IFN competent primary sheep endothelial cells. Our data showed that multiple segments were involved in decreased efficiency of BTV8H replication in cells in an IFN-induced antiviral state. Moreover, we examined changes in viral population diversity that occured after BTV-8 isolation in insect cells (Culicoides, KC) and after passage in mammalian cells and linked decreased diversity with BTV virulence in vivo. We found, that in general, the number of genetic variants was higher in BTV-8 before cell passaging, or after one passage in KC cells, compared to the number observed after even a single passage in BHK-21 cells. The highest total number of variants was found in virus passaged in KC cells, which suggests that insect vector might serve as an amplifier of quasispecies diversity of BTV. Together, these findings suggest that the virulence of BTV is a multifactorial phenomenon involving many aspects of virus-host interactions and it is not only affected by changes in the viral proteins selected at the consensus level, but also by the genetic variability of the population as a whole.
17
Connolly, John. "Analysis of Staphylococcus aureus virulence determinants". Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/12109/.
Abstract (sommario):
The success of the pathogen Staphylococcus aureus lies in its array of virulence determinants, which enable pathogenesis. The recent identification of novel S. aureus virulence determinants led to the hypothesis that there are more to be found. In silico analysis of the S. aureus genome identified three staphylococcal superantigen-like proteins (SSL12, SSL13 & SSL14), incorrectly annotated in the genome database as hypothetical proteins. Production of recombinant SSL12, 13 & 14 proteins gave a low yield of soluble protein, which precluded biochemical analysis. A genetic approach was taken and a triple gene deletion mutant constructed. No role for the 3 SSLs was found in an in vivo infection model, or in in vitro phagocytosis assays. However, a subtle reduction in growth in human blood, associated with the cellular component of blood was seen when compared with the wild-type. A genome-wide library of 1,920 strains each with a separate gene disrupted by a transposon (Tn) insertion was screened on human blood agar. Both the purine (purA and purB) and tetrahydrofolate (THF; pabA) synthesis pathways were found to be important for growth on human blood, but, in the case of the pabA disrupted strain, not on human plasma. THF is a single carbon donor/acceptor in many S. aureus biosynthesis pathways, and its synthesis is the target of sulphonamide antibiotics. The human blood phenotype for pabA was linked to dTTP synthesis, which is formed via a THF-dependent pathway, or a THF-independent pathway requiring the enzyme Tdk. As the pabA mutant can grow on human plasma it was hypothesised that Tdk is inhibited by a factor in the cellular component of blood, which leads to a requirement for dTTP. This suggests that the activity of sulphonamide drugs is the result of inhibition of THF coupled with the inhibition of Tdk by an as yet unknown factor present in human blood.
18
Rudd, Matthew Francis, e mikewood@deakin edu au. "Virulence determinants of infectious bursal disease virus". Deakin University. School of Biological and Chemical Sciences, 2003. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20050825.103742.
Abstract (sommario):
The very virulent (vv) pathotype of infectious bursal disease virus (IBDV) has spread rapidly throughout Europe, Asia, and the Middle East. Although Australia is currently unaffected, there remains the potential for incursion of an exotic isolate. The aim of this study was to identify putative virulence determinants of IBDV to facilitate the development of improved diagnostic assays for detection and characterisation of vvIBDV isolates.
Sequencing of Indonesian vvIBDV Tasik94 revealed a unique substitution
[ A¨S222] in the hypervariable region (HVR) of viral protein (VP) VP2, which did not appear to impinge on virulence or antigenicity. Phylogenetic analyses indicated that Tasik94 was closely related to Asian and European vvIBDV strains. Extensive alignment of deduced protein sequences across the HVR of VP2 identified residuesI242 I256 and I294 as putative markers of the vv phcnotype.
Comparison of the pathology induced by mildly-virulent Australian IBDV 002/73 and Indonesian vvIBDV Tasik94, revealed that histological lesions in the spleen, thymus and bone marrow were restricted to Tasik94-infected birds, suggesting the enhanced pathogenicity of vvIBDV might be attributed to replication in non-bursal lymphoid organs.
The biological significance of the VP2 HVR in virulence was assessed using recombinant viruses generated by reverse genetics. Both genomic segments of Australian IBDV 002/73, and recombinant segment A constructs in which the HVR of 002/73 was replaced with the corresponding region of either tissue culture-adapted virus or vvIBDV (Tasik94), were cloned behind T7 RNA polymerase promoter sequences. In vitro transcription/translation of each construct resulted in expression of viral proteins. Co-transfection of synthetic RNA transcripts initiated replication of both tissue culture-adapted parental and recombinant viruses, however attempts to rescue non-adapted viruses in specific-pathogen-free (SPF) chickens were unsuccessful.
Nucleotide sequence variation in the HVR of VP2 was exploited for the development of a new diagnostic assay to rapidly detect exotic IBDV isolates, including vvIBDV, using reverse transcription polymerase chain reaction (RT-PCR) amplification and Bmrl restriction enzyme digestion. The assay was capable of differentiating between endemic and exotic IBDV in 96% of 105 isolates sequenced to date.
19
Skinner, Anita Claire. "Molecular determinants of virulence in Leishmania mexicana". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337830.
20
Lewis, David Arthur. "Potential virulence determinants in Haemophilus ducreyi infection". Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341930.
21
Boonchai, S. "The virulence determinants of uropathogenic Escherichia coli". Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354421.
22
Harvey, Philippa Caroline. "Determinants of survival and virulence of Campylobacter". Thesis, Open University, 2000. http://oro.open.ac.uk/58052/.
Abstract (sommario):
The pathogenesis of Campylobacter enteritis is not well understood including the mechanisms involved in invasion and translocation across intestinal epithelial cells. The genetic make-up of the pathogen and its responses to different environmental cues are thought to contribute to the organism's ability to survive and cause disease. The extremes of environment which Campylobacter can with-stand, and the effect that this has on virulence and invasive ability remains undefined. For the first time, several isolates were compared quantitatively to determine the extent to which intracellular invasion contributes to translocation across epithelial cell mono layers. Translocation ability did not correlate with intracellular invasiveness, suggesting that different "invasion" phenotypes exist among Campylobacler isolates. Repeated exposure of Campylobacler isolates to Caco-2 cells caused an increase in their ability to invade and survive, which was associated with changes in protein expression. Campylobacler was grown in continuous culture under conditions of iron sufficiency, iron limitation, oxidative stress and low pH. Uniquely, growth under oxidative stress and iron replete conditions caused an increase in the invasive ability of C. jejuni 81116, which was correlated with the up-regulation of specific proteins. The role of three proteins, HtrB, Tpx and PEB-4, was investigated at the molecular level. Two of the encoding genes, peb4A and hlrB, were found to be essential for viability. Homologous recombination of an inactivated Ipx gene into the genome of C. jejuni caused increased sensitivity to H20 2, but did not affect the ability of C. jejuni to invade and survive within Caco-2 cell monolayers. This study demonstrated that isolates of Campylobacter differ significantly in their virulence potential with respect to their invasive phenotypes. In addition Campylobacler grown in well defined continuous culture conditions demonstrated for the first time the importance of iron and oxidative stress as acting as potenital cues for the expression of survival and invasion determinants.
23
Steggles, James Robert. "Virulence determinants and pathogenesis of Bacillus thuringiensis". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614837.
24
Mottola, Carla. "Virulence characterization and antimicrobial resistance of major bacterial genera from diabetic foot infections". Doctoral thesis, Universidade de Lisboa, Faculdade de Medicina Veterinária, 2017. http://hdl.handle.net/10400.5/14119.
Abstract (sommario):
Tese de Doutoramento em Ciências Veterinárias na especialidade de Ciências Biológicas e BiomédicasDiabetes mellitus is a major chronic disease that continues to increase significantly. One of the most important and costly complications of diabetes is the development of foot ulcers, colonized by pathogenic and antimicrobial resistant bacteria, which may be responsible for impairing its successful treatment. Diabetic foot ulcer (DFU) bacterial communities can be organized in polymicrobial biofilms, which may be responsible for its chronicity. The ability of these communities to produce biofilm was evaluated and was higher when compared to biofilm formation by individual species. Staphylococcus aureus is one of the most prevalent species in diabetic foot infections (DFI). Staphylococci isolated from DFU in patients from the Lisbon area were identified, genotyped and screened for virulence and antimicrobial resistance traits. The isolates showed high genomic diversity, were resistant to important clinically antibiotics and expressed relevant virulence determinants. As biofilm formation is one of the most important virulence traits of S. aureus, the antimicrobial susceptibility patterns of biofilm-producing S. aureus strains were also analysed. The minimum biofilm inhibitory and eradication concentrations were determined for ten antimicrobial compounds. Staphylococci biofilms were resistant to antibiotic concentrations ten to thousand times higher than those effective for planktonic cells. Furthermore, the enterococci frequently isolated from DFI, were also identified and characterized, showing high antimicrobial resistance and important virulence traits. Since DFI are often caused by resistant bacteria, it is necessary to find alternatives to antibiotic therapy, such as phage therapy. The inhibitory potential of five bacteriophages, previously characterized, was evaluated against established biofilms formed by S. aureus, P. aeruginosa and A. baumannii. A significant cell reduction after phage exposure was observed, mainly after multiple treatments. DFI are very complex and studies on this topic are scarce. It is necessary to intensify research in order to develop more adequate therapeutic protocols for this type of infection.
RESUMO - Caracterização da virulência e resistência a antimicrobianos dos principais géneros bacterianos envolvidos em infeções de pé diabético - Diabetes mellitus é uma doença crónica com grande impacto em saúde pública e cuja incidência continua a aumentar significativamente em todo o mundo, atingindo atualmente mais de 400 milhões de pessoas. Uma das complicações mais importantes da diabetes e associada a gastos económicos significativos são as úlceras de pé diabético. Uma vez que a camada protetora de pele é danificada, os tecidos profundos ficam expostos à infeção bacteriana, a qual pode evoluir rapidamente. As infeções das úlceras de pé diabético são a causa mais comum de internamento hospitalar de pacientes diabéticos e uma importante causa de morbilidade, levando frequentemente à amputação dos membros inferiores. Estas infeções podem ser promovidas por bactérias potencialmente patogénicas e resistentes aos compostos antimicrobianos, prejudicando assim o sucesso do tratamento. As comunidades bacterianas presentes nas úlceras podem estar organizadas em biofilmes polimicrobianos, que contribuem para que as infeções se tornem crónicas e muito difíceis de resolver. Foi avaliada a capacidade de produção de biofilme por comunidades polimicrobianas de isolados bacterianos de pé diabético, utilizando um ensaio de microtitulação em placa com “Alamar Blue” (AB) e uma técnica de Hibridação In Situ Fluorescente Múltipla (MFISH). Esta avaliação foi realizada em três períodos de incubação distintos (24, 48 e 72 horas), depois da determinação da capacidade de formação de biofilme por 95 isolados de úlceras de pé diabético pertencentes a vários géneros bacterianos (Staphylococcus, Corynebacterium, Enterococcus, Pseudomonas e Acinetobacter). Todos os isolados apresentaram a capacidade de produzir biofilme às 24 horas, sendo que a quantidade de biofilme produzido aumentou com o tempo de incubação. Pseudomonas apresentou a capacidade mais elevada de produção de biofilme, seguida de Corynebacterium, Acinetobacter, Staphylococcus e por fim, Enterococcus. Foram encontradas diferenças estatisticamente significativas na capacidade de formação de biofilme entre os três períodos de incubação. As comunidades polimicrobianas produziram mais biofilme do que as espécies individualmente. As comunidades formadas por Pseudomonas + Enterococcus, Staphylococcus + Acinetobacter e Corynebacterium + Staphylococcus formaram mais biofilme do que as comunidades formadas por Enterococcus + Staphylococcus e por Enterococcus + Corynebacterium. O comportamento biológico das diferentes espécies bacterianas nos biofilmes polimicrobianos tem implicações clínicas muito importantes para o sucesso do tratamento deste tipo de infeções. A sinergia entre as bactérias presentes em biofilmes multiespécies foi descrita previamente, sendo que este trabalho representa o primeiro estudo sobre a evolução temporal da formação de biofilme por parte de comunidades polimicrobianas isoladas de úlceras de pé diabético, incluindo várias espécies. [...]
Centro de Investigação Interdisciplinar em Sanidade Animal” (CIISA) of Faculty of Veterinary Medicine, University of Lisbon, Portugal
N/A
25
Moore, Jane. "Putative bacteroides fragilis virulence determinants; analysis and comparison". Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486575.
Abstract (sommario):
Bacteroidesfragilis forms part of the gastrointestinal microbiota. On release from the gastrointestinal tract this opportunistic pathogen can cause internal abscesses and bacteraemia. Completed genome sequences of B. fragi/is NCTC 9343, 638R and YCH46 recently became available. Therefore the importance of potential virulence factors may be assessed though genotypic and phenotypic comparisons. B. fragilis NCTC 9343 phase variably expresses a large capsule (LC), small capsule (SC) and an antigenically variable electron dense layer (EDL). A small irregular LC like capsule is expressed by B. fragilis 638R, attributed to a stop codon within BF2782 (putative polysaccharide export protein). Phase variable LC expression may be regulated by excision/insertion of a transpos~n, detected in PS-9/I of B. fragilis YCH46. The EDL polysaccharides produced by the 3 strains are divergent. This has no effect on in vivo survival. The conservation of invertible promoter regions (fIX sites) and putative transcriptional regulators, upxZ and upxY, indicates antigenic variation may be important for virulence. Invertases, finA and finB are involved in inversion of the fIX sites. The presence of . finA is conserved but notfinB. A long delay is observed prior to detection of antigenic variation in finB+ B. fragilis NCTC 9343, but not finE B. fragilis LS66. Therefore finB may be repressing inversion of the fix sites. The absence offinB, LC expression, haemagglutination phenotype, or reduced growth rate in a minimal medium does not affect in vivo survival. Iron acquisition and regulatory systems are important for B. fragilis virulence, with the ferric uptake protein, FeoAB, and ferric uptake regulator, Fur, required for B. fragilis survival in vivo. FeoAB is important for growth of B. fragilis in vitro, indicating ferrous iron is an important iron source. The haem uptake protein, HutA, and the peroxide regulon repressor, Per, are not required for B. fragilis survival in vivo.
26
Lam, T. H. Jason, e 林梓軒. "The study of virulence determinants of mycobacterium tuberculosis". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47849757.
Abstract (sommario):
Persistence in human macrophages is central to the virulence of Mycobacterium
tuberculosis, which is the causative agent of tuberculosis. Although the
intracellular parasitism is apparent, molecular determinants of mycobacterial
virulence are not well understood.
The current investigation identified virulent genes of M. tuberculosis by
measuring survivability of Mycobacterium smegmatis recombinants inside a
human monocytic cell line THP-1 after acquiring various virulent gene candidates
of M. tuberculosis. These gene candidates included nine virulent gene
candidates suggested by other studies, five genomic polymorphisms identified in
hypervirulent strains of M. tuberculosis using microarray-based comparative
genomic hybridization, and ten single nucleotide polymorphisms identified in the
hypervirulent strains using full genome sequencing. Interestingly, only
recombinants harboring a truncated Rv2820c and a known virulent gene mce1A
survived significantly better than vector control after six hours of ex vivo
infection.
As nucleotide sequencing indicated that the truncated Rv2820c loses around 60%
of gene at 3’ end, ex vivo survivability of M. smegmatis recombinants harboring
the last 60% of Rv2820c as well as the intact Rv2820c was measured, but was
similar to that of vector control. The 3’ truncated portion itself did not alter
mycobacterial survivability ex vivo, but its presence did compromise the survival
advantage gained due to the truncated Rv2820c.
To determine whether the truncated and the intact Rv2820c could enhance
mycobacterial virulence in vivo, these two alleles were transformed into
Mycobacterium marinum and their recombinants were used to infect zebrafish.
In vivo infection showed that zebrafish infected with the recombinant harboring
truncated Rv2820c died significantly faster than vector control, whereas the
recombinant harboring intact Rv2820c behaved similarly to vector control.
Results indicated that the truncated Rv2820c, but not the intact Rv2820c, could
enhance mycobacterial virulence both ex vivo and in vivo.
Additional nucleotide sequencing revealed that the 3’ truncation in Rv2820c is
caused by a Beijing/W-defining deletion RD207 and is commonly found in
Beijing/W strains of M. tuberculosis. Non-Beijing/W strains possess the intact
Rv2820c conversely. Since Beijing/W strains have proven to be more virulent
than non-Beijing/W strains both ex vivo and in vivo, the truncated Rv2820c may
be one of the Beijing/W-specific virulence determinants.
To confirm that Rv2820c of Beijing/W strains really enhances M. tuberculosis
survival in human macrophages, the truncated Rv2820c was transformed into
non-Beijing/W M. tuberculosis strains and their recombinants were used to infect
THP-1 cells. Ex vivo infection confirmed that the truncated Rv2820c could
enhance M. tuberculosis survival inside human macrophages, but is unlikely to
induce a different profile of cytokine secretion from infected macrophages.
In conclusion, the current study demonstrated that the truncated Rv2820c of
Beijing/W strains could enhance mycobacterial virulence both ex vivo and in vivo.
Enhanced phenotypic virulence, however, was not observed for the intact
Rv2820c of non-Beijing/W strains. The truncated Rv2820c may be one of the
Beijing/W-specific virulence determinants and collaboratively contribute to the
high phenotypic virulence of this family.published_or_final_version
Microbiology
Doctoral
Doctor of Philosophy
27
Yasir, Muhammad. "Regulation of virulence determinants in enteroaggregative Escherichia Coli". Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7251/.
Abstract (sommario):
Enteroaggregative Escherichia coli (EAEC) is an important human pathogen, which causes diarrhoeal disease. EAEC strains have many virulence determinants such as the fimbrial adhesins, dispersin, plasmid encoded toxin and Type VI secretion systems (T6SS). A typical pathogenic EAEC strain also possesses the transcriptional regulator, AggR (the aggregation regulator), which regulates the transcription of many virulence associated genes. How, AggR achieves this is still unclear. Thus, our objective was to identify the AggR-dependent promoters, which control the expression of the fimbrial genes, dispersin and the T6SS in EAEC strain 042 and the fimbrial genes in EAEC 17-2. In this study, AggR-dependent fimbrial promoters, from EAEC 042 and 17-2, were located and their transcription start sites identified upstream of the fimbrial operons on plasmids pAA2 and pAA, respectively. AggR-regulated fimbrial promoters were also identified upstream of aap, present on pAA2, and aaiA, present on the chromosome. AggR-binding sites and promoter elements were investigated using deletion analysis and site directed mutagenesis. The rules of AggR-dependent activation were studied by transplanting the AggR-binding site from the aafD promoter into an AggR-independent promoter to generate a suite of a semi-synthetic promoters. Moreover, mutagenesis of aggR itself was carried out, revealing that the N-terminus of AggR is important for transcription activation. This study has enabled us to better understand AggR-dependent transcription activation in this important bacterial pathogen.
28
Pemberton, Clare Louise. "Virulence determinants and their regulation in Erwinia carotovora". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614742.
29
Hapeshi, Alexia. "Chromosomal and plasmid determinants of Rhodococcus equi virulence". Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/17281.
Abstract (sommario):
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.
30
Li, Alice Hoy Lam. "Identification of virulence determinants of Mycobacterium tuberculosis via genetic comparisons of a virulent and an attenuated strain of Mycobacterium tuberculosis". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/596.
Abstract (sommario):
Candidate virulence genes were sought through the genetic analyses of two strains of Mycobacterium tuberculosis, one virulent, H37Rv, one attenuated, H37Ra. Derived from the same parent, H37, genomic differences between strains were first examined via two-dimensional DNA technologies: two-dimensional bacterial genome display, and bacterial comparative genomic hybridisation. The two-dimensional technologies were optimised for mycobacterial use, but failed to yield reproducible genomic differences between the two strains. Expression differences between strains during their infection of murine bone-marrow-derived macrophages were then assessed using Bacterial Artificial Chromosome Fingerprint Arrays. This technique successfully identified expression differences between intracellular M. tuberculosis H37Ra and H37Rv, and six candidate genes were confirmed via quantitative real-time PCR for their differential expression at 168 hours post-infection. Genes identified to be upregulated in the attenuated H37Ra were frdB, frdC, and frdD. Genes upregulated in the virulent H37Rv were pks2, aceE, and Rv1571. Further qPCR analysis of these genes at 4 and 96h post-infection revealed that the frd operon (encoding for the fumarate reductase enzyme complex or FRD) was expressed at higher levels in the virulent H37Rv at earlier time points while the expression of aceE and pks2 was higher in the virulent strain throughout the course of infection. Assessment of frd transcripts in oxygen-limited cultures of M. tuberculosis H37Ra and H37Rv showed that the attenuated strain displayed a lag in frdA and frdB expression at the onset of culture when compared to microaerophilic cultures of H37Rv and aerated cultures of H37Ra. Furthermore, inhibition of the fumarate reductase complex in intracellular bacteria resulted in a significant reduction of intracellular growth. Microarray technology was also applied in the expression analysis of intracellular bacteria at 168h post-infection. Forty-eight genes were revealed to be differentially expressed between the H37Ra and H37Rv strains, and a subset were further analysed via qPCR to confirm and validate the microarray data. phoP was expressed at a lower level in the attenuated M. tuberculosis H37Ra, whereas members of the phoPR regulon were up-regulated in the virulent H37Rv. Additionally, a group of genes (Rv3616c-Rv3613c) that may associate with the region of difference 1 were also up-regulated in the virulent H37Rv.
31
Abdullah, Abdallah Ibansharred. "Virulence determinants of aeromonads and other gram-negative bacteria". Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275038.
32
Dziva, Francis. "Virulence determinants of pasteurella multiocida with bovine haemorrhagic septicaemia". Thesis, Royal Veterinary College (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265334.
33
Turner, Lauren. "Identification of Virulence Determinants for Streptococcus sanguinis Infective Endocarditis". VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1560.
Abstract (sommario):
Streptococcus sanguinis is the second most common causative agent of bacterial infective endocarditis (IE). Risk of S. sanguinis IE is dependent on pre-disposing damage to the heart valve endothelium, which results in deposition of clotting factors for formation of a sterile thrombus (referred to as vegetation). Despite medical advances, high mortality and morbidity rates persist. Molecular characterization of S. sanguinis virulence determinants may enable development of prevention methods. In a previous screen for S. sanguinis virulence determinants by signature-tagged mutagenesis (STM) an attenuated mutant was identified with a transposon insertion in the nrdD gene, encoding an anaerobic ribonucleotide reductase. Evaluation of this mutant, as well as an nrdD in-frame deletion mutant, JFP27, by a soft-agar growth assay confirmed the anaerobic growth sensitivity of these strains. These studies suggest that an oxygen gradient occurs at the site of infection which selects for expression of anaerobic-specific genes at the nexus of the vegetation. The random STM screen failed to identify any favorable streptococcal surface-exposed prophylactic candidates. It was also apparent that additional genetic tools were required to facilitate the in vivo analyses of mutant strains. As it was desirable to insert antibiotic resistance markers into the chromosome, we identified a chromosomal site for ectopic expression of foreign genes. In vitro and in vivo analyses verified that insertion into this site did not affect important cellular phenotypes. The genetic tools developed facilitated further in vivo screening of S. sanguinis cell wall-associated (Cwa) protein mutants. A directed application of STM was employed for a comprehensive analysis of this surface protein class in the rabbit model of IE. Putative sortases, upon which Cwa proteins are dependent for cell surface localization, were also evaluated. No single S. sanguinis Cwa protein was determined essential for IE by STM screening; however competitiveness for colonization of the infection site was reduced for the mutant lacking expression of sortase A. The studies described here present a progressive picture of S. sanguinis IE, beginning with surface protein-dependent colonization of the vegetation in early IE, that later shifts to a bacterial persistence in situ dependent on condition-specific housekeeping genes, including nrdD.
34
Turner, Lauren Senty. "Identification of virulence determinants for streptococcus sanguinis infective endocarditis /". Online version not available until 8/4/2013, 2008. http://hdl.handle.net/10156/2243.
35
Agena, Mahmoud B. "Neonatal exposure to pathogens : determining key virulence factors". Thesis, Nottingham Trent University, 2017. http://irep.ntu.ac.uk/id/eprint/32859/.
Abstract (sommario):
The neonatal stage is the most critical period for infections, with mortality rate of up to 45% amongst children under five years. The genus Cronobacter has been involved in many outbreaks in neonatal intensive care units, with recorded meningitis, bacteraemia, and necrotizing enterocolitis (NEC). Although this genus was deeply investigated in vitro with different cell lines, until now, few researches have been focused on the use of H4 cell line, which is supposed to be more representative of neonatal response. Therefore, the present PhD study aimed to investigate the interaction of selected clinical isolates and the seven-type species of the genus Cronobacter, as well as one E. coli K1 isolate with H4 cells compared with Caco-2 cell line. Physiological analyses revealed most of the strains to be motile, and capsule and biofilm producers. A link between capsule production and serum resistance was shown by some strains. Strains were examined regarding their attachment, invasion, translocation and cytotoxicity as well as for the role of host cytoskeleton in the invasion process to both cell lines. All strains, especially C. sakazakii ST12 (696 and 703) were significantly more adhesive to the H4 than Caco-2 cells; this sequence type has previously been associated with neonatal NEC. Importantly, this study indicated that some clinical strains were more invasive to H4 than Caco-2 cells such as C. sakazakii 767 (meningitis) and 701 (NECIII). Moreover, attachment and invasion of E.coli were higher in H4 than Caco-2 cells. High attachment and invasion is potentially linked with excessive inflammatory response and NEC development in neonates. Most studied strains were able to translocate human cell lines, causing necrotic damage in the polarized monolayer. More importantly, translocation of blood or meningitic isolates such as C. sakazakii 709, C. malonaticus 1569, C.turicensis 564 was higher via H4 compared with Caco-2 cells. However, translocation of E. coli K1 strain 939 was similar in both cell lines. Most of the bacterial strains were cytotoxic to both cell lines and C. sakazakii ST3 strain 798 showed an ability to kill H4 cells up to 90-fold of blank, and about 70-fold when co-cultured with Caco-2 cells. Results suggests that intact bacterial cells that able to produce new proteins while in direct contact with the host cells is essential for the cytotoxicity, indicating the potential involvement of an active secretion system in cytotoxicity. Cytochalasin D and Colchicine mostly inhibited invasion to the H4 cells and enhanced the invasion of some strains to Caco-2 up to five-fold. Only Nocodazole significantly enhanced the invasion of some strains to H4 cell, and variably effected strains’ invasion to Caco-2. Data obtained from human cytoskeleton inhibitors experiments suggested the possible strain specific role of inhibitors on both cell lines, and strains may encode different pathways for uptake, with the possible involvement of eukaryotic receptors that recognize the invading bacteria. This study indicated that the response of the H4 cells to bacterial challenge and production of inflammatory cytokines was higher than Caco-2 cells. The H4 cells produced more IL-1-β, IL-4, IL-6, IL-8, IP-10, MCP-1, and EGF-α. Furthermore, tested strains (n=12) variably affected the expression of human Toll-like receptors (TLRs) and NF-kB subunits 1 and 2 in both cell lines, only C. sakazakii strain 709 upregulated expression of TLR1-4 in H4 cells and was the strongest inducer of receptor gene expression in both cell lines. More importantly, the upregulation of NF-kB subunits 1 is more likely related to the increased inflammatory cytokine production, while no link with subunit 2. However, TLR-1 was not expressed in Caco-2 in response to these strains, which needs further investigation. The effect of the E. coli K1 strain 939 on the TLRs expression was varied and no specific pattern was detected, but in some cases it showed similarity to the effect of C. sakazakii 767 which is also linked with neonatal meningitis. As most of the investigated bacterial strains displayed virulence factors with H4 cells closely related to their clinical pathology, the present study provides an important initial work to introduce H4 cells as a new modle for neonatal cell lines to analyse neonatal infections.
36
Fletcher, Jonathan Nigel. "Plasmid-encoded virulence determinants of an enteropathogenic (0111) Escherichia coli". Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316601.
37
Farrant, Jayne Lisa. "Molecular characterisation of the virulence determinants of enteropathogenic Escherichia coli". Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385084.
38
Haycocks, James Richard John. "Regulating expression of virulence determinants in enterotoxigenic Escherichia coli H10407". Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5650/.
Abstract (sommario):
Enterotoxigenic Escherichia coli (ETEC) is a major cause of traveller’s and infantile diarrhoea in developing countries, and results in considerable mortality in under 5 year olds. Disease is mediated through adhesion of ETEC cells to the intestinal brush border and the secretion of the heat-stable and/or heat-labile toxin. Whilst the toxins have been well studied it is still not clear how their expression is regulated. This work has defined binding of CRP, H-NS and σ\(^7\)\(^0\) across the genome of the prototypical ETEC strain H10407. We demonstrate a central role for all three factors in regulating pathogenicity in ETEC H10407. Hence, we show that CRP directly regulates expression of both \(estA2\) and \(estA1\), which encode the heat-stable toxins. Furthermore, CRP indirectly represses expression of the heat-labile toxin. This work also identifies a role for CRP in controlling transcription of a small open reading frame, imbedded within a gene, at the 3’ end of an operon encoding a type I secretion system.
39
Ireri, Ricki Gatumu. "Studies on some determinants of virulence in Alcelaphine herpesvirus 1". Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/29817.
Abstract (sommario):
Malignant catarrhal fever (MCF) is a fatal lymphoproliferative of Artiodactyla. The disease is caused by infection of susceptible hosts with one of two, gammaherpesviruses, Alcelphine herpesvirus-1 (AHV-1) or Ovine herpesvirus-2 (OHV-2). On primary isolation AHV-1 infectivity is cell-associated and the virus can induce MCF following susceptible into susceptible hosts. Cell free virus which is pathogenic for cattle is observed following low serial passage of the virus in cell cultures. After further serial passage cell free virus is observed, but this virus cannot produce disease experimentally. AHV-1 genomic rearrangement occur during the transition from virulence to attenuation. Two genes, encoding putative protein 5 (P-5) and protein 1 (P-1), are truncated during this rearrangement. Sequence encoding each of these proteins was cloned and the proteins expressed in vitro. Rabbits, a laboratory model for AHV-1, were successfully immunised with these proteins. Neither of these proteins however induced a protective immune response. Although both proteins are expressed in vitro transcripts for these proteins could not be detected in vivo in animals reacting with MCF. During the course of this study, the complete sequence of the AHV-1 genome was published. P-1 and P-5 were shown to form part of ORF 50 and A7 respectively. These ORFs were therefore reassessed to determine their positions in the attenuated and virulent virus. New isolates were obtained from cattle showing clinical MCF and also from wildebeest. Viral DNA derived from new isolates has shown that ORF 50 and ORF A7 are conserved between isolates and the virulent laboratory adapted isolate. The results presented here show that a block of sequence, which includes sequence for ORF 50 and its promoter are translocated from a position in the middle of the unique NDA to a terminal position where it is inverted with respect to its transcriptional orientation in the virulent virus. The ORF is transcriptionally silent in the attenuated virus and the results presented here show that this is due to the inactivity of the truncated ORF 50 promoter in the attenuated virus.
40
MacFarlane, Ryan Cousteau. "Identification of virulence determinants in the protozoan parasite entamoeba histolytica /". May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
41
Hyatt, Doreene Rose. "The hemolysins produced by Serpulina hyodysenteriae as putative virulence determinants". Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187349.
Abstract (sommario):
Serpulina hyodysenteriae is the etiological agent of swine dysentery (SD). The hemolysin produced by this spirochete is believed to be a virulence factor of the bacteria. Muir et aI. (78) have recently cloned a gene (tlyA) from S. hyodysenteriae responsible for the expression of a hemolysin protein. The B204 RNA-core extract and recombinant hemolysins were active at temperatures ranging from 27-42 °C and pH ranges of three to nine. There was no inhibitory effect by calcium, magnesium, BSA, sucrose or 50 mM EDTA while both zinc and copper were inhibitory. The activity of the two hemolysins could be partially blocked by components with a diameter of 2.0-2.3 nm. Neutralization of the hemolysins by newborn but not fetal bovine serum was observed. Cholesterol and cholesterol derivatives were able to partially block the hemolytic activity. To test the mode of activity of the hemolysins, sheep erythrocytes were internally labeled with ⁸⁶rubidium. The release of both hemoglobin and ⁸⁶rubidium from the erythrocytes were compared after exposure to the B204 RNA-core hemolysin. It was found that ⁸⁶rubidium was released after 2 minute exposure to the hemolysin. Hemoglobin was released at 4 minutes of exposure, indicating that the hemolysin lyses the erythrocytes using a porin mechanism. T/yA-minus mutants of two S. hyodysenteriae strains (B204 and C5) were tested for virulence in pigs. None of the animals inoculated with the mutant strains developed SD. Inoculation of pigs with the wild-type B204 or C5 strain produced SD in 100% and 60% respectively. Pigs infected with the mutant strains were further tested for susceptibility to challenge with the wild-type strain B204. After challenge, 50% of the pigs previously inoculated with the B204 tlyA -minus mutant were protected, whereas all of the control pigs contracted SD. None of the pigs previously inoculated with the C5 tlyA-minus mutant, developed SD upon challenge with the B204 wild-type strain, whereas 40% of the control pigs developed SD in this experiment. Thus the tlyA encoded hemolysin of S. hyodysenteriae appears to be an important virulence factor in SD and previous colonization with tlyA -minus mutants provides partial protection to challenge with a virulent strain.
42
Kanvil, Sadia. "Pea aphid virulence factors determining compatibility with Medicago truncatula". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/39392.
43
Kamran, Mohammed Farakh. "The identification and isolation of putative virulence determinants of Candida glabrata". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409177.
44
QUILICI, MARIE-LAURE. "Les determinants plasmidiques impliques dans la virulence et l'immunogenicite des yersinia". Paris 7, 1992. http://www.theses.fr/1992PA077162.
Abstract (sommario):
La virulence des yersinia associee a la presence d'un plasmide dont la taille varie de 42 a 47 mda. Ce travail montre que des souris primo-infectees par y. Enterocolitica ne sont resistantes a la peste que si la souche vaccinale est porteuse d'un plasmide. Le fait que cette protection croisee necessite la presence du plasmide chez y. Enterocolitica indique que ces genes de virulence sont probablement impliques dans la multiplication bacterienne chez l'hote. Nous avons etudie les homologies de sequence par hybridation selon la methode de southern entre les plasmides des souches de y. Enterocolitica induisant une protection croisee et le plasmide de virulence de y. Pestis. Ces hybridations montrent que les homologies sont reparties sur une grande partie de la molecule plasmidique, 13 fragments de restrictions par l'endonuclease bam h1 du plasmide de 47 mda de y. Pestis hybrident avec le plasmide de y. Enterocolitica o:9 utilise comme sonde. Cette etude genetique a ete elargie a d'autres plasmides de yersinia, comme y. Pseudotuberculosis ou y. Ruckeri. L'etude des proteines codees par ces plasmides a confirme ces resultats: les produits codes par le plasmide de y. Enterocolitica sont reconnus par un serum anti-y. Pestis. Ces proteines sont donc rapidement immunogenes et impliques dans l'induction de cette immunite croisee. Une nouvelle approche a ete developpee dans ce travail, permettant la detection de ces antigenes directement dans des tissus infectes
45
Brown, Meredith A. "Genetic determinants of virulence in emerging viruses of natural felid populations". Diss., Connect to online resource - MSU authorized users, 2008.
Abstract (sommario):
Thesis (Ph. D.)--Michigan State University. Dept. of Fisheries and Wildlife, 2008.Title from PDF t.p. (viewed on April 1, 2009) Includes bibliographical references (p. 101-117). Also issued in print.
46
Feavers, L. M. "The biological properties and genetic determinants of virulence factors of Escherichia coli". Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370615.
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Wilson, Lynn Margaret. "Physiological studies on swarming and production of virulence determinants in Clostridium septicum". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627209.
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Wallace, Nathan Christopher. "Metabolic and Physiological Determinants in Listeria monocytogenes Anaerobic Virulence Regulation". University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1543424768026244.
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Perry, Kyle James. "Differential fluorescence-based genetic screens to identify novel Listeria monocytogenes virulence determinants". Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226063.
Abstract (sommario):
Listeria monocytogenes is a Gram-positive, facultative intracellular pathogen that causes gastroenteritis, which in the young, the elderly, and the immunocompromised can progress to severe invasive disease with high mortality. While previous studies have largely elucidated the bacterial and host mechanisms necessary for the bacterium to access its replicative niche in the host cell cytosol, the L. monocytogenes factors required for adaptation to life within this restrictive environment are poorly understood. In this dissertation, I
describe a fluorescence-activated cell sorting (FACS)-based differential
fluorescence genetic screening technique for the identification of L.
monocytogenes genes necessary for optimal intracellular replication. Bacteria harboring deletions in identified genes were defective for intracellular replication,
plaque formation, and in vivo virulence, validating the ability of the screening method to identify novel intracellular replication-defective mutants. Minor alteration of the FACS-based screening strategy allowed the detection and differentiation of bacterial mutants displaying varying severities of actin-based motility defects. A preliminary FACS-based genetic screen to identify actin-based
motility mutants isolated multiple independent insertions within internal control genes, demonstrating the potential utility of FACS-based differential fluorescence genetic screening methods for the identification of L. monocytogenes genes important for multiple virulence phenotypes. Lastly, my characterization of the X-prolyl
aminopeptidase PepP, a novel virulence factor identified by the FACS-based genetic screen to discover genes necessary for optimal intracellular replication, revealed this enzyme plays an unexpected role in L. monocytogenes virulence gene regulation.
50
Hariri, S. H. "Identification of the virulence determinants of the neonatal meningitic bacterium Cronobacter sakazakii". Thesis, Nottingham Trent University, 2015. http://irep.ntu.ac.uk/id/eprint/27928/.
Abstract (sommario):
The Cronobacter genus is a member of the family Enterobacteriaceae, comprising of seven species C. sakazakii, C. malonaticus, C. turicensis, C. dublinensis, C. muytjensii, C. universalis, and C. condimenti. Cronobacter is gaining importance as a pathogen due to the severity of the infection caused such as septicaemia, necrotizing entercolitis and severe infantile meningitis, and the numerous outbreaks reported. Clinical cases are associated with the three species C. malonaticus, C. turicensis and, in particular, with C. sakazakii multilocus sequence type 4. The understanding of its pathogenicity is still not fully understood despite the clinical evidence, resulting in the concern the FAO-WHO. Therefore, this study aimed to apply the Multiple Locus Sequence Typing scheme (MLST) to three collections of clinical strains which had not been previously profiled by MLST. These were from USA (2011), Israel (2000), and the Czech Republic (2007-2012). The strains from the latter two collections had only been identified as E. sakazakii, at that point. Among the Israeli strain collection, isolates from infants ranging from 2 to 36 weeks old, 7/9 strains were identified as belonging to the ST4 clonal complex. Similarly, 10/15 of the C.sakazakii strains isolated from US infant cases were found to belong to the ST4 clonal complex. Whereas 11 strains of the Czech isolates were from various age groups and were identified as C.malonaticus especially ST7, which is also the most clinically predominant ST of that species among non-infant infections and 6 strains were found to belong ST4. This research reported the first meningitis case by Cronobacter malonaticus (CC112) which was from an infant (age < 1 month) with severe brain damage which led to their death. Of particular interest in this research was the finding that C. sakazakii and some strains of C. turicensis were unique in the Cronobacter genus in utilization of exogenous sialic acid as a carbon source which may have a role in the organism’s virulence. The presence of sialic acid utilization genes could be relatively recent evolution, as high levels of sialic acid are accessible to bacteria in intestinal mucosa and the brain. Another important finding was, the presence of a number of key virulence associated genes assessed by laboratory studies in Cronobacter sakazakii strains (in particular with ST4). In this study, 36 clinical isolates were analysed that included: two iron acquisition system gene clusters (eitA and iucC), a pla- like homologue named Cronobacter plasminogen activator (Cpa) ,and type VI secretion (T6SS) gene cluster. The majority of C. sakazakii strains were serum resistant (32/36), and thus, they had the ability to survive in blood by preventing serum-mediated killing. Also, different iron acquisition systems were encoded by C. sakazakii 97% to attain iron from the host. Some C. sakazakii strains encoding T6SS patterns were from of clinical cases such as NECII and severe meningitis strains Plasmid profiling experiments were carried out on the Cronobacter sakazakii strains sequenced in a parallel study. The high-size plasmid (molecular weight between 138 and 118 kb) was observed as common in (27/34) of all strains which known to encode an assortment of virulence factors. Also, plasmid DNA analysis publicised that there was no specific plasmid profiling among clinical strains. Furthermore, it shown there is no correlation observed between sequence type and present or absent the plasmid. Furthermore, it was of interest whether the presence of plasmid pESA3 is linked with virulence in C. sakakzaii. This research work developed a tool by inserting the plasmid pESA3 into a plasmid-less strain and observeing the significance changes in the phenotypic and virulence associated behaviour. Stains encoding large plasmid were able to invade human intestinal epithelial cells Caco-2, brain endothelial cells HBMEC and rBCEC4. Also have been reported significant observation in siderophore production and serum survival values whereas plasmid less strain and not shown less significant associated virulence.