Auswahl der wissenschaftlichen Literatur zum Thema „Bacterial disinfection mechanisms“

Experiments showed that attachment of bacteria to surfaces provided the greatest increase in disinfection resistance. Attachment of high nutrient grown, unencapsulated, Klebsiellapneumoniae to glass microscope slides afforded the microorganisms as much as a 150 fold increase in disinfection resistance. Other mechanisms which increased disinfection resistance included: the age of the biofilm, bacterial encapsulation and previous growth conditions (e.g. growth medium, and growth temperature). These factors increased chlorine resistance from two to ten fold. The choice of disinfectant residual was shown to influence the type of resistance mechanism observed. Disinfection by free chlorine was affected by surfaces, age of the biofilm, encapsulation and nutrient effects. Disinfection by monochloramine, however, was only affected by surfaces. Importantly, the research showed that these resistance mechanisms were multiplicative (e.g. the resistance provided by one mechanism could be multiplied by the resistance provided by a second). These results provide important insights to understand the survival of bacteria in chlorinated drinking water supplies.

In this comparative study, the impact of two microbial protective mechanisms against simulated UVA disinfection was assessed by using protocols previously developed for UVC disinfection assays. (i) The impact of natural microorganism aggregation and attachment to particles was assessed by targeting total coliform bacteria in natural surface water samples. (ii) The impact of bacteria internalisation by zooplankton was assessed by using C. elegans nematodes as a model host and E. coli as a bacterial target for UVA inactivation. Dispersion of natural aggregates by blending prior to UVA exposure was shown to enhance the inactivation rate of total coliforms as compared to untreated raw water. Removal of particles by an 8-μm membrane filtration did not improve UVA disinfection efficiency. Twenty-four per cent of the highest applied UVA fluence was found to reach internalised E. coli in nematodes. Both aggregation and internalisation showed similar impact as protective mechanisms against UVA and UVC bacterial inactivation.

Microbial water pollution is a key concern leading to waterborne diseases. This study evaluated the disinfection of wastewater using ozonation. The following aspects were investigated: inactivation efficiency against <i>Escherichia coli, Salmonella</i> species, <i>Shigella</i> species, and <i>Vibrio cholerae</i>; modelling of inactivation kinetics using disinfection models; and evaluation of microbial regrowth studies. 99% bacterial inactivation was obtained within 15 min, irrespective of the water matrix, showing the strong oxidizing potential of ozone. The disinfection data were fitted into the log-linear and Weibull models. The survival curves were non-linear and fitted the Weibull model (fractional bias and normalized mean square error equal to 0.0), especially at high bacterial concentrations (10⁶ CFU/mL). The inactivation occurred in two stages: an initial rapid stage (15 min) and a final slow stage exhibiting a tailing mechanism (15-45 min) probably as a result of the self-defence mechanisms adopted by the bacteria to limit oxidative stress. Considering the pattern of survival curves, no significant differences (<i>p</i> > 0.05) were observed among the four tested bacterial species; thus showing that ozone was effective against all the bacteria tested. There was minimal bacterial regrowth in the treated samples 24 h after ozone disinfection with reactivation values of 0-5% obtained.

ABSTRACTIt is increasingly clear that bacteria manage to evade killing by antibiotics and antimicrobials in a variety of ways, including mutation, phenotypic variations, and formation of biofilms. With recent advances in understanding the dynamics of the tolerance mechanisms, there have been subsequent advances in understanding how to manipulate the bacterial environments to eradicate the bacteria. This study focuses on using mathematical techniques to find the optimal disinfection strategy to eliminate the bacteria while managing the load of antibiotic that is applied. In this model, the bacterial population is separated into those that are tolerant to the antibiotic and those that are susceptible to disinfection. There are transitions between the two populations whose rates depend on the chemical environment. Our results extend previous mathematical studies to include more realistic methods of applying the disinfectant. The goal is to provide experimentally testable predictions that have been lacking in previous mathematical studies. In particular, we provide the optimal disinfection protocol under a variety of assumptions within the model that can be used to validate or invalidate our simplifying assumptions and the experimental hypotheses that we used to develop the model. We find that constant dosing is not the optimal method for disinfection. Rather, cycling between application and withdrawal of the antibiotic yields the fastest killing of the bacteria.

Disinfection kinetics has been well established for selected antimicrobial agents on isolated bacterial strains. Due to the difficulties of culturing most bacteria, the majority of these studies have been limited to readily cultivable microorganisms of a single type or family. This study explores the feasibility of using flow cytometry for characterising the disinfection kinetics and minimum inhibitory concentration (MIC) of an Escherichia coli culture and a microbial consortium. The proposed method relies on fluorescent dye molecules to indicate the morphological and physiological status of numerous individual cells. Biocides of varying effectiveness and inactivation mechanisms (chlorine, iodine, and silver) were used to evaluate this novel application. Using pseudo-first-order kinetics, the coefficients of specific lethality of chlorine and iodine on Escherichia coli were 4.71 and 3.78×10−3 L mg−1 min−1 and MIC of silver ion was between 60 and 80 μg L−1. The coefficients of specific lethality of chlorine and iodine on the microbial consortium were 4.96 and 8.89×10−3 L mg−1 min−1 and MIC of silver ion was between 40 and 60 μg L−1. This method can be used to provide a rapid and consistent way of determining disinfection kinetics and MICs for pure and mixed bacterial cultures and can potentially be used to examine water and wastewater disinfection efficiency. However, caution should be used to ensure that the physiological and morphological status characterised by cytodyes is a result of the inactivation mechanisms of the disinfectants evaluated.

Recent molecular studies on endophytic bacterial diversity have revealed a large richness of species. Endophytes promote plant growth and yield, suppress pathogens, may help to remove contaminants, solubilize phosphate, or contribute assimilable nitrogen to plants. Some endophytes are seed-borne, but others have mechanisms to colonize the plants that are being studied. Bacterial mutants unable to produce secreted proteins are impaired in the colonization process. Plant genes expressed in the presence of endophytes provide clues as to the effects of endophytes in plants. Molecular analysis showed that plant defense responses limit bacterial populations inside plants. Some human pathogens, such as Salmonella spp., have been found as endophytes, and these bacteria are not removed by disinfection procedures that eliminate superficially occurring bacteria. Delivery of endo-phytes to the environment or agricultural fields should be carefully evaluated to avoid introducing pathogens.

Photoelectrocatalysis is a hybrid photon/electron-driven process that benefits from the synergistic effects of both processes to enhance and stabilize the generation of disinfecting oxidants. Photoelectrocatalysis is an easy to operate technology that can be scaled-up or scaled-down for various water treatment applications as low-cost decentralized systems. This review article describes the fundamentals of photoelectrocatalysis, applied to water disinfection to ensure access to clean water for all as a sustainable development goal. Advances in reactor engineering design that integrate light-delivery and electrochemical system requirements are presented, with a description of photo-electrode material advances, including doping, nano-decoration, and nanostructure control. Disinfection and cell inactivation are described using different model microorganisms such as E. coli, Mycobacteria, Legionella, etc., as well the fungus Candida parapsilosis, with relevant figures of merit. The key advances in the elucidation of bacterial inactivation mechanisms by photoelectrocatalytic treatments are presented and knowledge gaps identified. Finally, prospects and further research needs are outlined, to define the pathway towards the future of photoelectrocatalytic disinfection technologies.

Abstract Waterborne diseases significantly affect human health and are responsible for high mortality rates worldwide. Antibiotics have been known for decades for treatment of bacterial strains and their overuse and irrational applications are causing increasing bacteria resistance. Therefore, there is a strong need to find alternative ways for efficient water disinfection and microbial control. Carbon nanotubes (CNTs) have demonstrated strong antimicrobial properties due to their remarkable structure. This paper reviews the antimicrobial properties of CNTs, discusses diverse mechanisms of action against microorganisms as well as their applicability for water disinfection and microbial control. Safety concerns, challenges of CNTs as antimicrobial agents and future opportunities for their application in the water remediation process are also highlighted.

Bacterial contamination of platelet concentrates (PCs) represents the highest post-transfusion infectious risk. The skin flora bacterium Staphylococcus epidermidis has been reported to be the predominant aerobic contaminant of PCs. The Ramirez' group has shown that S. epidermidis can form surface-attached bacterial aggregates known as biofilms, and can outcompete other coagulase-negative staphylococci, such as Staphylococcus capitis, in PCs. The ability of S. epidermidis to form biofilms has been linked to increased pathogenicity and missed detection during PC screening with an automated culture system (BacT/ALERT). This thesis aimed at investigating the proliferative advantage and resistance mechanisms displayed by S. epidermidis in the PC milieu. Furthermore, in an effort to enhance PC safety for transfusion patients, I studied the anti-biofilm properties of essential oils and antimicrobial peptides (AMPs). My studies aimed at improving PC safety by focussing on both the point of introduction of bacterial contaminants (blood collection), and the stage at which bacterial contaminants can form biofilms and proliferate (PC storage). S. epidermidis can be found in the skin of blood donors as biofilms, which are resistant to the blood donor skin disinfectant currently used by Canadian Blood Services, chlorhexidine-gluconate and isopropyl alcohol (CHG-IPA). Here, several plant-extracted essential oils were evaluated for their ability to enhance the anti-biofilm activity of CHG-IPA. Data revealed that the Lavandula multifida oil and its main component (linalool) greatly enhanced the activity of CHG-IPA against S. epidermidis biofilms. Furthermore, the ability of a combination of three synthetic AMPs to inhibit S. epidermidis biofilm formation during PC storage was assessed These results showed that the combination of AMPs could inhibit biofilm formation but was ineffective against pre-formed S. epidermidis biofilms. The accumulation associated protein (Aap) encoded by the aap gene, found in most S. epidermidis strains and absent in S. capitis, plays a role in biofilm formation. When S. epidermidis aap is transformed into S. capitis, this bacterium displayed increased biofilm formation and proliferated to higher concentrations compared to untransformed S. capitis and to a S. epidermidis aap deletion mutant. Based on these results, aap appears to play a role in providing S. epidermidis a proliferative advantage in PCs by enhancing biofilm formation. Lastly, the GraRS system and SepA were studied for their role in S. epidermidis resistance to platelet-derived AMPs using the synthetic AMP PD4 as a model molecule. Results indicate that the GraS mechanism is involved in resistance towards PD4. The work presented in my thesis provides further insights into why S. epidermidis has a proliferative advantage in the PC storage environment and allows for the proposal of alternative methods to enhance PC safety for transfusion patients.

在過去的幾十年中，人們越來越關心由致病微生物引起的水傳播疾病的爆發。作為一種綠色技術，太陽能光催化在不引起二次污染的殺滅各種致病微生物方面引起了廣泛關注。但是，目前最廣泛應用的TiO₂光催化劑僅在紫外光激發範圍內有效，而紫外光僅占太陽光譜的4%。因為太陽光譜中有45%是可見光，所以新型可見光催化劑的開發是現今光催化技術亟待解決的問題。另一方面，目前對於光催化殺菌機理的研究報導非常稀少而且主要集中于紫外-TiO₂光催化系統中，而對於可見光催化系統中的殺菌機理研究還鮮有報導。
本研究介紹三種新型可見光催化劑的殺菌性能。它們是B,Ni共摻TiO₂微米球（BNT），BiVO₄納米管（BV-NT）和CdIn₂S₄微米球（CIS）。其中一種是修飾的TiO₂催化劑，另兩種是新型的非TiO₂基催化劑。採用加入各種湮滅劑結合一種分離裝置的研究方法系統研究了三種催化劑的可見光殺菌機理。首先，研究發現當用BNT作為光催化劑的時候，可見光催化降解染料和殺菌之間存在巨大的差異。對於光催化降解染料，光催化反應主要發生在催化劑的表面，是由表面活性物質如h⁺, ・OHs和・O₂⁻參與，而細菌可以被擴散物種如・OH[subscript b]和H₂O₂，以不直接接觸催化劑表面的方式被殺死。可擴散的H₂O₂在這種殺菌過程中起了最重要的作用，而它可以在催化劑價帶以・OH[subscript b]溶液體相耦合和・OH[subscript s]催化劑表面耦合兩種方式產生。
其次，在用BV-NT作為光催化劑可見光殺滅大腸桿菌的過程中，光生空穴（h⁺）以及由空穴產生的氧化物種，如・OH[subscript s], H₂O₂和・HO₂/・O₂⁻，是主要的活性物種。但是這個殺菌過程只有很少量的H₂O₂可以擴散到溶液中，導致有效殺菌需要細菌和光催化表面直接接觸。研究還發現，細菌本身可以捕獲光生電子（e⁻）來降低空穴-電子複合率，這個作用在無氧氣參與的殺菌過程中尤為明顯。透射電鏡顯示，細菌的破壞是由細胞壁開始從外到內的被破壞。研究認為，表面羥基・OH[subscript s]比溶液體相羥基・OH[subscript b]更加重要，並且很難從BV-NT表面擴散進容易中。
最後，研究還發現CIS也具有不接觸細菌而有效可見光催化殺滅大腸桿菌的能力，這也歸結為可擴散H₂O₂，而不是・OH的作用。H₂O₂可以通過・O₂⁻從催化劑導帶和價帶同時產生。本研究提供了幾種具有應用前景的高效可見光催化殺菌催化劑，並對其光催化機理提出了新的思路，指出可見光催化殺菌機理與使用的光催化劑是密切相關的。更重要的是，本研究建立了一種簡便易行的研究方法，可用於對其他各種可見光催化殺菌系統進行深入的機理研究。
During the last few decades, there has been an increasing public concern related to the outbreak of waterborne diseases caused by pathogenic microorganisms. As a green technology, solar photocatalysis has attracted much attention for the disinfection of various microorganisms without secondary pollution. However, the most commonly used TiO₂ photocatalyst is only active under UV irradiation which accounts for only 4% of the solar spectrum. Therefore, new types of photocatalysts that can be excited by visible light (VL) are highly needed, as 45% of the solar spectrum is covered by VL. In addition, existing reports on the mechanisms of photocatalytic bacterial disinfection are rather limited and mostly based on TiO₂-UV irradiated systems, thus the mechanisms in visible-light-driven (VLD) photocatalystic disinfection systems are far from fully understandable.
In this study, three different kinds of VLD photocatalysts were discovered for the photocatalytic bacterial disinfection. They were B-Ni-codoped TiO₂ microsphere (BNT), bismuth vanadate nanotube (BV-NT), and cadmium indium sulfide (CIS). One was modified TiO₂-based photocatalyst, and the other two were new types of non-TiO₂ based photocatalyst. The mechanisms of VLD photocatalytic disinfection were investigated by multiple scavenging studies combined with a partition system. Firstly, significant differences between VLD photocatalytic dye decolorization and bacterial disinfection were found in the case of BNT as the photocatalyst. For photocatalytic dye decolorization, the reaction mainly occurred on the photocatalyst surface with the aid of surface-bounded reactive species (h⁺, ・OH[subscript s] and ・O₂⁻), while bacterial cell could be inactivated by diffusing reactive oxidative species such as ・OH[subscript b] and H₂O₂ without the direct contact with the photocatalyst. The diffusing H₂O₂ played the most important role in the photocatalytic disinfection, which could be produced both by the coupling of ・OH[subscript b] in bulk solution and ・OH[subscript s] on the surface of photocatalyst at the valence band.
Secondly, when using BV-NT as the photocatalyst for Escherichia coli K-12 inactivation, the photogenerated h⁺ and reactive oxidative species derived from h⁺, such as ・OH[subscript s], H₂O₂ and ・HO₂/・O₂⁻, were the major reactive species. However, the inactivation requires close contact between the BV-NT and bacterial cells, as only a limited amount of H₂O₂ can diffuse into the solution to cause the inactivation. The bacterial cells can trap e⁻ in order to minimize e⁻-h⁺ recombination, especially under anaerobic condition. Transmission electron microscopic study indicated the destruction process of bacterial cell began from the cell wall to other cellular components. The ・OH[subscript s] was postulated to be more important than ・OH[subscript b] and was not supposed to be released very easily from BV-NT surface.
Finally, it was found that E. coli cells could be effectively inactivated without the direct contact with CIS, which was attributed to the function of diffusing H₂O₂ rather than ・OH. H₂O₂ was produced from both conduction and valance bands with the involvement of ・O₂⁻, which were detected by ESR spin-trap with DMPO trapping technology. While this study provided promising candidates of efficient VLD photocatalysts for water disinfection as well as deep insights into the disinfection mechanisms, it was notable that the photocatalytic disinfection mechanisms were quite dependent on the selected photocatalysts. Nevertheless, the research methodology established in this study was proved to be facile and versatile for the in-depth investigation of mechanisms in different VLD photocatalyst systems.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Wang, Wanjun.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 140-170).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Acknowledgements --- p.i
Abstract --- p.vi
List of Figures --- p.xvi
List of Plates --- p.xxiii
List of Tables --- p.xxiv
List of Equations --- p.xxv
Abbreviations --- p.xxvii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Water disinfection --- p.1
Chapter 1.2 --- Traditional water disinfection methods --- p.2
Chapter 1.2.1 --- Chlorination --- p.2
Chapter 1.2.2 --- Ozonation --- p.3
Chapter 1.2.3 --- UV irradiation --- p.4
Chapter 1.3 --- Advanced oxidation process --- p.5
Chapter 1.4 --- Photocatalysis --- p.6
Chapter 1.4.1 --- Fundamental mechanism for TiO₂ photocatalysis --- p.7
Chapter 1.4.2 --- Photocatalytic water disinfection --- p.12
Chapter 1.5 --- Visible-light-driven photocatalysts for water disinfection --- p.16
Chapter 1.5.1 --- Modified TiO₂ photocatalysts --- p.16
Chapter 1.5.1.1 --- Surface modication of TiO₂ by noble metals --- p.16
Chapter 1.5.1.2 --- Ion doped TiO₂ --- p.18
Chapter 1.5.1.3 --- Dye-sensitized TiO₂ --- p.19
Chapter 1.5.1.4 --- Composite TiO₂ --- p.20
Chapter 1.5.2 --- Non-TiO₂ based photocatalysts --- p.22
Chapter 1.5.2.1 --- Metal oxides --- p.22
Chapter 1.5.2.2 --- Metal sulfides --- p.24
Chapter 1.5.2.3 --- Bismuth metallates --- p.25
Chapter 1.6 --- Photocatalystic disinfection mechanisms --- p.27
Chapter 2 --- Objectives --- p.30
Chapter 3 --- Comparative Study of Visible-light-driven Photocatalytic Mechanisms of Dye Decolorization and Bacterial Disinfection by B-Ni-codoped TiO₂ Microspheres --- p.32
Chapter 3.1 --- Introduction --- p.32
Chapter 3.2 --- Experimental --- p.35
Chapter 3.2.1 --- Materials --- p.35
Chapter 3.2.2 --- Characterizations --- p.36
Chapter 3.2.3 --- Photocatalytic decolorization of RhB --- p.36
Chapter 3.2.4 --- Photocatalytic disinfection of E. coli K-12 --- p.37
Chapter 3.2.5 --- Partition system --- p.40
Chapter 3.2.6 --- Scavenging study --- p.41
Chapter 3.2.7 --- Analysis of ・OH and ・O₂⁻ --- p.42
Chapter 3.2.8 --- Analysis of H₂O₂ --- p.43
Chapter 3.3 --- Results and Discussion --- p.44
Chapter 3.3.1 --- XRD and SEM images --- p.44
Chapter 3.3.2 --- Photocatalytic decolorization of RhB --- p.46
Chapter 3.3.2.1 --- Role of reactive species --- p.46
Chapter 3.3.2.2 --- Partition system for dye decolorization --- p.49
Chapter 3.3.3 --- Photocatalytic bacterial disinfection --- p.51
Chapter 3.3.3.1 --- Role of reactive species --- p.51
Chapter 3.3.3.2 --- Partition system for bacterial disinfection --- p.54
Chapter 3.3.3.3 --- pH effects --- p.58
Chapter 3.3.3.4 --- Role of H₂O₂ --- p.60
Chapter 3.3.4 --- Role of ・O₂⁻ in RhB decolorization and bacterial disinfection --- p.67
Chapter 3.4 --- Conclusions --- p.75
Chapter 4. --- Visible-light-driven Photocatalytic Inactivation of E. coli K-12 by Bismuth Vanadate Nanotubes: Bactericidal Performance and Mechanism --- p.76
Chapter 4.1 --- Introduction --- p.76
Chapter 4.2 --- Experimental --- p.78
Chapter 4.2.1 --- Materials --- p.78
Chapter 4.2.2 --- Photocatalytic bacterial inactivation --- p.80
Chapter 4.2.3 --- Bacterial regrowth ability test --- p.82
Chapter 4.2.4 --- Analysis of reactive species --- p.82
Chapter 4.2.5 --- Preparation procedure for bacterial TEM study --- p.83
Chapter 4.2.6 --- Analysis of bacterial catalase activity --- p.84
Chapter 4.2.7 --- Analysis of potassium ion leakage --- p.84
Chapter 4.3 --- Results and Discussion --- p.85
Chapter 4.3.1 --- Photocatalytic bacterial inactivation --- p.85
Chapter 4.3.2 --- Mechanism of photocatalytic inactivation --- p.87
Chapter 4.3.2.1 --- Role of primary reactive species --- p.87
Chapter 4.3.2.2 --- Role of direct contact effect --- p.96
Chapter 4.3.3 --- Destruction model of bacterial cells --- p.98
Chapter 4.3.4 --- Analysis of radical production --- p.104
Chapter 4.4 --- Conclusions --- p.109
Chapter 5 --- CdIn₂S₄ Microsphere as an Efficient Visible-light-driven Photocatalyst for Bacterial Inactivation: Synthesis, Characterizations and Photocatalytic Inactivation Mechanisms --- p.111
Chapter 5.1 --- Introduction --- p.111
Chapter 5.2 --- Experimental --- p.113
Chapter 5.2.1 --- Synthesis --- p.113
Chapter 5.2.2 --- Characterizations --- p.114
Chapter 5.2.3 --- Photocatalytic bacterial inactivation --- p.116
Chapter 5.3 --- Results and Discussion --- p.117
Chapter 5.3.1 --- Characterizations of Photocatalyst --- p.117
Chapter 5.3.2 --- Photocatalytic bacterial inactivation and mechanism --- p.121
Chapter 5.3.3 --- Destruction process of bacterial cell --- p.128
Chapter 5.3.4 --- Analysis of radical generation --- p.131
Chapter 5.4 --- Conclusions --- p.133
Chapter 6 --- General Conclusions --- p.135
Chapter 7 --- References --- p.140