Thesis (M.S.)--University of Michigan, 1947. / eContent provider-neutral record in process. Description based on print version record.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 85-92). Also available in electronic version.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-86).

Listeria monocytogenes is a rod-shaped Gram positive bacterium. It generally exist ubiquitously in nature, where it lives as a saprophyte. Occasionally it however enters the food chain, from where it can be ingested by humans and cause gastro-intestinal distress. In immunocompetent individuals L. monocytogenes is generally cleared within a couple of weeks, but in immunocompromised patients it can progress to listeriosis, a potentially life-threatening infection in the central nervous system. If the infected individual is pregnant, the bacteria can cross the placental barrier and infect the fetus, possibly leading to spontaneous abortion. The infectivity of L. monocytogenes requires a certain set of genes, and the majority of them is dependent on the transcriptional regulator PrfA. The expression and activity of PrfA is controlled at several levels, and has traditionally been viewed to be active at 37 °C (virulence conditions) where it bind as a homodimer to a “PrfA-box” and induces the expression of the downstream gene. One of these genes is ActA, which enables intracellular movement by recruiting an actin polymerizing protein complex. When studying the effects of a blue light receptor we surprisingly found an effect of ActA at non-virulent conditions, where it is required for the bacteria to properly react to light exposure. To further study the PrfA regulon we tested deletion mutants of several PrfA-regulated virulence genes in chicken embryo infection studies. Based on these studies we could conclude that the chicken embryo model is a viable complement to traditional murine models, especially when investigating non-traditional internalin pathogenicity pathways. We have also studied the effects of small molecule virulence inhibitors that, by acting on PrfA, can inhibit L. monocytogenes infectivity in cell cultures with concentrations in the low micro-molar range.

Intestinal dwelling parasites live in close association with the complex microbiota that inhabit our intestinal tracts. The intestinal helminth, Trichuris muris, depends on these bacteria for egg hatching and successful establishment of infection within the epithelium of the caecum and colon. Infection causes significant alterations to the host intestinal microbiota, including a decrease in bacterial diversity and shifts in proportions of certain bacterial groups. This is accompanied by a decrease in Foxp3+ regulatory T cells and changes to the metabolic potential of the host microbiota, consequently impacting host health. However, the factor(s) driving these changes and the existence and role of its own intestinal microbiota is unknown. Infection of C57BL/6 and immunodeficient SCID mice with a high dose (~ 200 embryonated eggs) and a low dose (~ 20 embryonated eggs) of T. muris was used to determine the impact of worm burden and the adaptive immune system on the host intestinal microbiota, in comparison to naïve controls. Microbiota analysis was performed by 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) and Illumina sequencing. This revealed that infection-induced microbiota changes were dose dependent and high level infection caused an increase in the Bacteroidaceae and Enterobacteriaceae families, independently of the host adaptive immune system. Development of a surface sterilisation protocol enabled the internal T. muris microbiota to be analysed by 16S rRNA gene DGGE and fluorescence in situ hybridisation (FISH). The resulting data indicated that T. muris requires its own diverse intestinal microbiota that is derived from, but distinct to, that of its host. A core microbiota is selected and maintained by the parasite regardless of the surrounding host microbiota. The parasite microbiota is important for its fitness, shown in vitro using an antibiotic motility assay and in vivo using germ free (GF) mice. Furthermore, infection with T. muris causes a significant reduction in caecal butyrate concentrations and consequently a decrease in the expression of butyrate transporters in caecal tissue. Interestingly, the T. muris microbiota is able to produce the short-chain fatty acid (SCFA) butyrate, which the parasite is unable to make itself yet secretes into its local environment. Together these strategies promote the long term survival of T. muris within the intestinal niche, adding a new level of complexity to the interaction between the pathogen, the host and their respective microbiotas that underpins successful chronic nematode infection.

No description available.

Objective: The objective of this thesis was to compare demographic and clinical characteristics and factors associated with advanced hepatic fibrosis between HIV and HIV-hepatitis B (HBV) co-infected patients. Methods: Proportional odds models were developed to investigate socio-demographic and clinical variables’ association on liver fibrosis determined by AST-to-Platelet-Ratio-Index (APRI). Results: HBV status and APRI values were available for 2,419 of 9,289 (26%) participants. 199 (9%) were HBV co-infected. Compared to HIV infected, HIV-HBV co-infected individuals were 2.19 (95% CI: 1.63, 2.90) and 1.68 (95% CI: 1.10, 2.53) times more likely to belong in a higher level of APRI category. Compared to HIV mono-infection, HIV-HBV co-infected participants on ARV therapy were less likely to have clinically significant or advanced fibrosis compared to mild or moderate fibrosis. Conclusion: We provide evidence in favour of an association between ARV therapy and reduced fibrosis in HIV-HBV co-infected population.

The most common type of adverse events in healthcare in Canada reported by the Canadian Institute for Health Information (CIHI) are nosocomial infections. Amongst nosocomial infections, implant associated infections have been reported to be most common. Despite having the implantation surgeries carefully performed, a small, but still considerable number of devices gets colonized by bacteria resulting in implant associated infections and/or surgical site infections. The patients are then started on high dose antibiotics, which if ineffective, is followed by reimplantation surgeries that leads to long hospital stays and detrimental effects in their lives. Due to this, an alternative to antibiotics is required which could prevent and/or treat bacterial colonization on implants. The main objective of this thesis was to demonstrate the effectiveness of an antimicrobial based CLKRS peptide capped silver nanoparticle coating on a metallic and polymeric based biomaterial used in various implantable medical devices. The CLKRS peptide capped silver nanoparticle formulation was specifically engineered and tested for its antibacterial and antibiofilm properties. Silver nanoparticles were synthesised by photochemical reduction of silver ions upon photocleavage of the photoinitiator I-2959. The metal nanostructure surfaces were protected with the CLKRS peptide and tested on planktonic and biofilms of P. aeruginosa, S. aureus and S. epidermidis. The bacterial quantification was done by survival colony counting. The cytotoxicity of the silver nanoparticle formulation was also tested on human dermal fibroblast, mouse bone marrow derived macrophages, and human epithelial cells by cell proliferation assay. Results show the formation of a nanometric layer of nanosilver on the surface of the material inhibiting the growth of bacteria and eradicating pre-existing biofilms with no significant cell toxicity suggesting the prepared formulation could be a useful tool in preventing and controlling infections on implants during surgery and post implantation. This technology thus could serve as an alternative therapy for surgical site infections and/or implant associated infections.

Methicillin-resistant Staphylococcus aureus is a leading cause of hospital infections world-wide. Consecutive S. aureus wound isolates (n=561) were collected from PHW Microbiology ABM Laboratory, Swansea (PHW-ABM); 137 (24.4%) were mecA-positive; 424 (75.6%) were mecA-negative using real-time PCR. Audit revealed that 15 (10.9%) mecA-positive strains were not reported as MRSA. Genotyping was performed using pulsed-field gel electrophoresis (PFGE), spa typing and SCCmec typing. MRSA predominantly belonged to EMRSA-15 (89.1% >) and EMRSA-16 (5.8%) clones. All S. aureus strains were included in an evaluation of three SCCmec-orfX PCR assays. The assays had high diagnostic sensitivity (>95%) and specificity (> 94% >) but false negative and false positive results were obtained. A deletion at the SCCmec-orfX right junction was proposed as the probable cause of false negative results. SCCmec-associated loci ccrAB1, ccrAB4, ccrC, and dcs were detected in four false positive MSSA, respectively. MALDI Biotyper mass spectrometry was evaluated for identification of S. aureus. Nineteen (3.4%) of the PHW-ABM wound isolates were Panton Valentine-Leukocidin (PVL)-positive S. aureus. The molecular epidemiology of these and PVL-positive S. aureus (n=61) from Specialist Antimicrobial Chemotherapy Unit, Cardiff (SACU) was investigated using mecA and arginine catabolic mobile element PCRs, PFGE, spa and SCCmec typing. The PHW-ABM strains were predominantly MSSA belonging to the CC159 (n=5; 26.3%), CC275 (n=4; 21.1%) and CC005 (n=2; 10.5%) spa-BURP clusters, affiliated to the ST121, ST30 and ST22 lineages. Within the SACU cohort the USA300 clone (n=16; 26.2%) was predominant, other genotypes included: t044- MRSA-IVc (n=5; 8.2%); t002-MRSA-IVc (n=3; 4.9%) and t127-MRSA-IVa (n=2; 3.3%), affiliated to the European (ST80), USA800 (ST5) and USA400 (ST1) clones. Susceptibility testing demonstrated statistically significant differences between the SACU and PHW-ABM cohorts for oxacillin 57%/5% >, gentamicin 2%/16%, and tetracycline 10% >/42% resistance (p < 0.05). These observed differences highlight the importance of including unselected strains in addition to referred reference laboratory isolates in epidemiological investigations.

No description available.