Phage infection reinstates antibiotic sensitivity in MDR Pseudomonas aeruginosa: A study on phage and bacterial evolution

The emergence of antibiotic resistance among bacterial pathogens is a significant public health threat affecting humans worldwide. In Europe, Pseudomonas aeruginosa contributes to almost 9% of overall multi-drug-resistant (MDR) infections. Alternative methods for controlling MDR pathogens have been explored for several decades. Bacteriophage therapy is one of the oldest and most efficient alternative solutions. The study described in this thesis began with the isolation and characterization of 25 MDR P. aeruginosa clinical strains and eigth novel lytic phages. The investigation disclosed the infection with two phage isolates, PIAS and PAPSZ1, led to the sequential appearance of phage-resistant colonies with two phenotypes (green and brown). We examined the evolutionary basis for the two types of mutants and uncovered phage mutants capable of infecting green mutants. Simultaneously we also learned that PIAS phage infected the host via the OrpM-MexXY system involved in drug efflux. Thus, the PIAS-resistant mutants decreased the minimum inhibitory concentrations (MIC) for several non-effective antibiotics. After this new insight into the evolutionary arms race between hosts and phages, we decided to use this window to comprehensively eradicate mutants by treating MDR strain with previously resistant antibiotics combined with PIAS phage. The in vitro study with PIAS phage-antibiotic combination completely prevented the formation and growth of mutants. We tested the same strategy in an in vivo rescue experiment in the mouse lung infection model, when combined with PIAS phage and fosfomycin. The combination therapy saved 75% of the animals. Later, we used PAPSZ1 phage to investigate whether phage mutants can suppress bacterial resistance. We isolated multiple PAPSZ1 mutants after a continuous infection cycle, which can block or suppress bacterial resistance and mutant formation and broaden the host specificity of the phages. Phages like PIAS and PAPSZ1 offer a unique window that can exploit to eradicate MDR bacteria. This study highlights the importance of preliminary and detailed examinations of phage-host bacterium interactions preceding the application of a given phage. The experimental data in this thesis shows that studying phage-host bacterium interactions and coevolution will help to utilize phage therapy’s full potential when treating MDR infections

Environmental and Economic Implications of Small-Scale Canadian Aquaponics: A Life Cycle Study

Agricultural production will be challenged in the near future to keep up with the rising nutritional demands of a growing global population. Additionally, climate change, through increased frequency of extreme weather events and droughts, will further push food production to its limits. Controlled-environment food production systems (CEFPS) are suggested as viable options to supplement existing agriculture by allowing food production expansion without requiring large amounts of land and by offering protection from changing weather patterns and other undesirable external conditions. Aquaponics is a form of CEFPS that combines recirculating aquaculture with hydroponics to produce both fish and vegetables. However, the environmental and economic performances of these systems in Canada and other cold climates have yet to be explored in depth. The overarching goal was to evaluate the potential for aquaponics to be a responsible and sustainable solution to maintaining Canadian food security. Specifically, this thesis aimed to identify environmental and economic barriers faced by small-scale Canadian aquaponics systems and provide options for reducing barriers and environmental impacts through the application of life cycle assessment (LCA) and life cycle cost (LCC) analysis. The major results of this study indicate that aquaponics in its current form is an energy-intensive form of agriculture and is more environmentally impactful than conventional forms of fish and vegetable production with a global warming potential (GWP) of 68 kg CO2eq/kg live fish and 50 kg CO2eq/kg leafy greens. Alternative scenarios, including energy efficiency improvements, renewable energy sources, and insect-based fish feed, were considered in order to address the environmental and economic hotspots identified. The following specific conclusions can be made: (1) energy consumption for artificial lighting and heating made necessary by cold climates is the biggest contributor to environmental impacts and costs; (2) an alternative scenario with off-site wind energy, LED lighting, and insulation reduces life cycle costs by 5% and GWP by 97%; and (3) alternative scenarios with insect-feed and on-site renewable energy can reduce specific environmental impacts but are more costly. It is recommended to pay particular attention to building design aspects, such as access to natural lighting and energy efficient HVAC systems, and climate-specific choices, such as cold-resistant crops and fish, in order to reduce the inherent energy intensity of operation. Overall, this work will help researchers and businesses improve performance of aquaponics systems, while serving as a foundation for the sustainability assessment of cold-climate aquaponics

Effect of silver content on the structure and antibacterial activity of silver-doped phosphate-based glasses

Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 µg·mm–2·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (20 µm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections

Prevalence of vancomycin-resistant Enterococci in India between 2000 and 2022: a systematic review and meta-analysis

Vancomycin-resistant Enterococci (VRE) infections are recurrently reported in different parts of India in the last two decades. However, an up-to-date, countrywide information concerning the prevalence and the rate of VRE in India is limited and hence this study aimed to estimate the pooled prevalence of VRE in India. Methods: A literature search was performed using various databases. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed throughout. Cross-sectional studies reporting the prevalence of VRE in India from human samples whereby at least two Enterococci were isolated between 1 January 2000 and 31 December 2022 were sought for inclusion. Data were extracted and analysed using Microsoft Excel and Comprehensive Meta-analysis version 4, respectively. Results: Nineteen studies were included in the analyses. A collective total of 3683 Enterococci isolates were examined, of which 368 were VRE strains. The pooled prevalence of VRE in India was calculated at 12.4% (95% CI: 8.6–17.5; Q = 189.69; I2 = 90.51%; p = < 0.001). E. faecalis was the most frequently isolated species (1450 [39.37%]) followed by E. faecium (724 [19.66%]). Amongst the VRE strains, E. faecium was the most prevalent (214 [58.15%]) followed by E. faecalis (134 [36.41%]). An upsurge in the rate of VRE infections was observed in India over time: VRE prevalence was estimated at 4.8% between 2000 and 2010 and 14.1% between 2011 and 2020. Conclusion: This study presents the most up-to-date information on the rate of VRE infections in India. Though lower than the findings for some less developed countries, VRE prevalence in India is notable and on the rise

Bismuthene nanosheets produced by ionic liquid assisted grinding exfoliation and their use for oxygen reduction reaction

We report the simple synthesis of bismuthene nanosheets (BiNS) by ionic liquid assisted grinding exfoliation, followed by size selection sequential centrifugation steps for the first time. The exfoliation process results in the formation of self-assembled spherule-like superstructures with abundant edge sites, which are able to catalyze the oxygen reduction reaction (ORR) via a two-electron pathway, with a higher efficiency than the bulk Bismuth. We rationalize the enhanced ORR activity of the BiNS to: (i) the presence of 1 dimensional topological edge states, which provide strong conduction channels for electron hopping between the bismuth layers and (ii) the more active role of edge sites in facilitating O(2) adsorption and dissociation of O–O bonds compared to the basal plane. The present study provides a pathway for employing 2D topological insulators as a new class of electrocatalysts for clean energy applications

The cariogenic effect of starch on oral microcosm grown within the dual constant depth film fermenter

Evidence on the link between starch intake and caries incidence is conflicting, therefore the cariogenicity of starch compared with sucrose was explored using a dual Constant Depth Film Fermenter (dCDFF) biotic model system. Bovine enamel discs were used as a substrate and the dCDFF was inoculated using human saliva. CDFF units were supplemented with artificial saliva growth media at a constant rate to mimic resting salivary flow rate over 14 days. The CDFF units were exposed to different conditions, 2 % sucrose or 2 % starch 8 times daily and either no additional fluoride or 1450 ppm F- twice daily. Bovine enamel discs were removed at intervals (days 3, 7, 10 and 14) for bacterial enumeration and enamel analysis using Quantitative Light Induced Fluorescence (QLF) and Transverse Microradiography (TMR). Results showed that in the absence of fluoride there was generally no difference in mineral loss between enamel exposed to either sucrose or starch when analysed using TMR and QLF (P > 0.05). In the presence of fluoride by day 14 there was significantly more mineral loss under starch than sucrose when analysed with TMR (P < 0.05). It was confirmed that starch and sucrose are similarly cariogenic within the dCDFF in the absence of fluoride. With the aid of salivary amylase, the bacteria utilise starch to produce an acidic environment similar to that of bacteria exposed to sucrose only. In the presence of fluoride, starch was more cariogenic which may be due to the bacteria producing a more hydrophobic intercellular matrix lowering the penetration of fluoride through the biofilm. This is significant as it indicates that the focus on sugars being the primary cause of caries may need re-evaluating and an increase in focus on carbohydrates is needed as they may be similarly cariogenic as sugars if not more so