Browsing by Author "Tucker, Keira"

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    Antibiotic resistance in surface waters and biofilm-response to environmental contaminants
    (Stellenbosch : Stellenbosch University, 2021-12) Tucker, Keira; Wolfaardt, Gideon M.; Botes, Marelize; Feil, Edward; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Ensuring water security for the future has become important due to rapid urbanisation and diminishing freshwater resources. South Africa’s water resources are scarce and as a result, reclamation of alternative freshwater resources such as treated wastewater is being investigated. There is growing evidence that drinking and wastewater treatment is either non- compliant to quality standards or lacking in certain communities. In areas with no infrastructure for wastewater removal, open sewers create a health risk for humans, animals, and the environment. Poor antimicrobial stewardship, over-use and incorrect disposal has led to increased resistance to antibiotics, rendering some bacterial infections untreatable. There is a concern that sub- inhibitory concentrations of antibiotics create a selection pressure that promotes horizontal gene transfer and emergence of bacterial communities that are resistant to antibiotics. Antibiotics, antibiotic resistant bacteria (ARB), as well as other contaminants that have been shown to promote antimicrobial resistance (AMR) such as heavy metals, enter surface waters and wastewater treatment works (WWTW) in trace concentrations via multiple pathways. As a result, WWTW are deemed hotspots for the emergence and dissemination of AMR. In addition, environmental waters are home to various matrices, including biofilms that are especially problematic in a clinical setting due to their antibiotic resistant and persistent nature. The research presented in this dissertation aimed to contribute to the knowledge surrounding the abundance of ARB in WWTW and surface waters in a South African context. Although ARB and antibiotic resistance genes (ARG) were detected in WWTW effluent, the abundance of both were reduced compared to the influent, suggesting that WWTW played a role in reducing AMR in receiving waters, while exposure to sub-inhibitory concentrations of antibiotics did not result in a significant change in the number of target ARG in isolates selected as representatives of a cultured population. This was emphasised in an expanded study that monitored various regions over a year. In addition, it was shown that surface waters, biofilms and sediments influenced by anthropogenic activities from residential and industrial sectors had higher prevalence of ARB compared to samples influenced by agricultural activity. Metagenomic analysis revealed that ARG relating to efflux pumps were the most common compared to those specific for target antibiotics. Due to heavy-metals and antibiotics being present in the environment in trace concentrations, exposure of mixed-community biofilms to sub-inhibitory concentrations of these contaminants was investigated. AMR in the biofilms did not increase, but it was suggested that the sub-inhibitory exposure promoted the development of persistent mixed community biofilms. Treatment interventions are crucial for removing pollutants and AMR already present in the environment. However, with due recognition of the complexity involved when considering humans, animals, the environment and a diverse pool of contaminants, this dissertation argues the need to expand the approach for mitigation of emergence or dissemination of AMR in the environment by incorporating greater emphasis on antibiotic stewardship, policies around antibiotic usage in all sectors, and overall public awareness.
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    Disinfectant, Soap or Probiotic Cleaning? Surface Microbiome Diversity and Biofilm Competitive Exclusion
    (MDPI [Commercial Publisher], 2020-11-04) Stone, Wendy; Tolmay, Janke; Tucker, Keira; Wolfaardt, Gideon M.
    This study extends probiotic cleaning research to a built environment. Through an eight-month cleaning trial, we compared the e ect of three cleaning products (disinfectant, plain soap, and a probiotic cleaner containing a patented Bacillus spore consortium), and tap water as the control, on the resident microbiome of three common hospital surfaces (linoleum, ceramic, and stainless steel). Pathogens, Escherichia coli and Staphylococcus aureus, were deposited and desiccated, and competitive exclusion was assessed for each microbiome. Cell survival was shown to be an incomplete tool for measuring microbial competitive exclusion. Biofilm competition offered a fuller understanding of competitive dynamics. A test for culturable cell survival showed that both plain soap and probiotic cleaner regimes established a surface microbiome that outcompeted the two pathogens. A different picture emerged when observing biofilms with a deposited and desiccated GFP-labeled pathogen, Pseudomonas aeruginosa. Competitive exclusion was again demonstrated. On surfaces cleaned with disinfectant the pathogen outcompeted the microbiomes. On surfaces cleaned with plain soap, the microbiomes outcompeted the pathogen. However, on surfaces cleaned with probiotic cleaner, despite the exponentially higher surface microbial loads, the microbiome did not completely outcompete the pathogen. Thus, the standard culturable cell test for survival on a surface confirmed the competitive advantage that is typically reported for probiotic cleaners. However, observation of competition in biofilms showed that the more diverse microbiome (according to alpha and beta indices) established on a surface cleaned with plain soap had a better competitive advantage than the monoculture established by the probiotic cleaner. Therefore, microbial diversity appears to be as critical to the competitive exclusion principle as cell numbers. The study showed that both plain soap and probiotic cleaner fostered competitive exclusion far more effectively than disinfectant. Probiotic cleaners with microbial diversity could be worth considering for hospital cleaning.