Browsing by Author "Kuster, Margot Ellen"

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    Evaluating antimicrobial resistance profiles, UV response, and curli production in Gram-negative river water isolates from the Cape Winelands
    (Stellenbosch : Stellenbosch University, 2024-03) Kuster, Margot Ellen; Sigge, G. O.; Lamprecht, Corne ; Rip, Diane ; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Resistance by pathogenic microorganisms to antimicrobial agents is rising, posing a threat to human health. Aquatic environments provide the ideal setting for the dissemination and acquisition of antibiotic resistance. Following contamination via irrigation water, fresh produce becomes an ideal vector for the spread of pathogenic and antibiotic resistant microorganisms. Globally, increased consumption of these often untreated foods raises the risk of foodborne illness and exposure to antibiotc residues. Water from certain rivers used for the irrigation of fresh produce in the Cape Winelands region has been identified as unsuitable for irrigation, with faecal coliform concentrations exceeding guidelines. Additionally, studies have identified antibiotic and multidrug resistant bacteria in these waters. Treatment of contaminated waters before irrigation is thus necessary. Ultraviolet (UV) irradiation has successfully inactivated pathogenic microorganisms, but its efficacy on antibiotic resistant bacteria varies. Litle is known about the impact of irradiation on the antibiotic resistance profiles of resistant bacteria, or how photoreactivation and dark repair influence these bacteria. Similarly, while surface adhesion and self-aggregation structures are thought to reduce efficacy in UV treatment of waters, limited literature is available to substantiate these claims. This study, therefore, aimed to establish extensive antibiotic resistance profiles of bacterial river water isolates from certain rivers sites in the Cape Winelands region and to determine the impact of UV irradiation on the antibiotic resistance profiles of these river water isolates. It also aimed to identify the presence of curli (a surface adhesion structure) within isolates to understand whether these may influence UV treatment. Extended-spectrum beta-lactamase (ESBL)-producers isolated by Oosthuizen (2022) originating from the Mosselbank, Franschhoek, Plankenburg, Eerste, and Jonkershoek rivers, and isolates exhibiting UV resistance following a recovery period isolated by Jankowitz (In press) from two locations on the Berg river and one location on the Eerste river were investigated. Bacterial identification testing revealed a prevalence of Escherichia coli in the rivers. Antibiotic susceptibility testing to 19 antibiotics revealed that ESBL-producers exhibited greater antibiotic resistances when compared to non-producers, and a link between ESBL- production and multidrug resistance (MDR) could be established. Resistances to ‘critically important’ and ‘highly important’ antimicrobials for human medicine, as classified by the WHO, were prevalent in both sets of isolates indicating potential misuse of these antimicrobials in the region. A subset of ESBL-producing E. coli with heightened antibiotic resistance (n=6), and non ESBL- producing E. coli with heightened antibiotic susceptibility which had previously exhibited UV resistance qualities (n=7) were further investigated. Isolates underwent an 80 mJ.cm⁻² low-pressure UV treatment followed by a recovery period, which yielded good log₁₀CFU.mL⁻¹ reductions (mean log₁₀CFU.mL⁻¹ reduction = 6.68). Survival following recovery was low, but results exhibited a trend of increased survival following light recovery when compared to dark recovery. Post-treatment enrichment was found to promote growth in isolates exhibiting low counts. UV irradiation at 80 mJ.cm⁻² had little impact on the antibiotic susceptibility profiles of the isolates, but changes in resistances to ‘critically’ and ‘highly’ important antimicrobials were seen. A high prevalence of curli fibre production was detected in the more antibiotic resistant ESBL-producing E. coli. Curli-producing isolates expressed curli at both 37°C and 26°C, a critical finding given the typical high summer temperatures and reliance on irrigation in the Cape Winelands region during the spring and summer seasons. Overall, the study confirmed the presence of antibiotic and multidrug resistance in bacteria isolated from certain rivers used for irrigation of fresh produce in the Cape Winelands region. UV irradiation at 80 mJ.cm⁻² was found to be a feasible water treatment technique to reduce E. coli concentrations to within irrigation water guidelines. While recovery was low in the isolates after UV treatment, findings highlight the need to consider the potential for recovery during storage and distribution. The link identified between antibiotic resistance and curli production in E. coli is concerning as irrigation using waters containing curli- producers could result in a heightened risk of exposure of fresh produce consumers to antimicrobial resistant bacteria.