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    Effects of selected emerging contaminants found in wastewater on antimicrobial resistance and horizontal gene transfer
    (Elsevier B.V., 2023-08-29) van Hamelsveld S; Jamali-Behnam F; Alderton I; Kurenbach B; McCabe AW; Palmer BR; Gutiérrez-Ginés MJ; Weaver L; Horswell J; Tremblay LA; Heinemann JA
    The widespread use of emerging contaminants (ECs) may be compounding the problem of antibiotic resistance. Various non-antibiotic pollutants have been shown to alter bacterial responses to antibiotics and increase horizontal transfer of antimicrobial resistance (AMR) genes. ECs include components of medicines, foods, disinfectants, personal care products and agrichemicals. ECs concentrate in some environments such as in wastewater, where the pollutants and pathogenic microorganisms mix. We investigated the effects on antibiotic resistance and gene transfer of nine ECs and one commercial product formulation (Roundup). We used the bacterium Salmonella enterica serovar Typhimurium and the antibiotics ampicillin and gentamicin as indicators of the effects of antibiotic-EC co-exposures. We measured intra- (Escherichia coli) and interspecies (E. coli x S. enterica) conjugation frequencies during exposure to ECs. Interestingly, the observed effect could change at different antibiotic concentrations. Exposures to increasing concentrations of ECs was associated with increased conjugative transmission within species, but rarely increased interspecies transmission. We report the first test ever of clotrimazole on AMR and horizontal gene transfer and a newly described effect of dimethyl sulfoxide (DMSO), often used as a solvent for organic compounds.
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    Monitoring the mode of action of synthetic and natural biocides against Aeromonas hydrophila by Raman spectroscopy and chemometrics
    (BioMed Central Ltd, 2021-12) Mehta M; Liu Y; Waterland M; Holmes G
    We have investigated the mode of action of synthetic biocides, (2-(thiocyanomethylthio) benzothiazole(TCMTB), dichlorophen, (commonly used in leather industry for preservation) and natural biocides, oregano and eucalyptus oils, on Aeromonas hydrophila using Raman spectroscopy in collaboration with multivariate analysis and 2D correlation spectroscopy to evaluate whether Raman spectra acquired contained valuable information to study the action of biocides on bacterial cells. The growth of A. hydrophila in clear and outer edge zone of inhibition differ in their reaction with different biocides, which allows us to highlight the differences as a characteristic of two kinds of bacteria. Such classification helps identify oregano oil as the most effective biocide by altering clear and outer edge zone of bacteria. Standard disk diffusion assay method was used for screening biocide bacteria interactions and later analysed by Raman spectroscopy. The paper also presents the introduction of TCMTB and oregano oil into leather processing stages to examine and determine the antimicrobial effect as an application to real-world setting. Therefore, we conclude that Raman spectroscopy with appropriate computational tools constitutes a powerful approach for screening biocides, which provide solutions to all the industries using biocides including leather industry, considering the potentially harmful effect of biocides to humans and the environment.