Browsing by Author "Kurenbach B"

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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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    Sublethal exposure to commercial formulations of the herbicides dicamba, 2,4-dichlorophenoxyacetic acid, and glyphosate cause changes in antibiotic susceptibility in Escherichia coli and Salmonella enterica serovar Typhimurium.
    (AMER SOC MICROBIOLOGY, 24/03/2015) Kurenbach B; Marjoshi D; Amábile-Cuevas CF; Ferguson GC; Godsoe W; Gibson P; Heinemann JA
    UNLABELLED: Biocides, such as herbicides, are routinely tested for toxicity but not for sublethal effects on microbes. Many biocides are known to induce an adaptive multiple-antibiotic resistance phenotype. This can be due to either an increase in the expression of efflux pumps, a reduced synthesis of outer membrane porins, or both. Exposures of Escherichia coli and Salmonella enterica serovar Typhimurium to commercial formulations of three herbicides-dicamba (Kamba), 2,4-dichlorophenoxyacetic acid (2,4-D), and glyphosate (Roundup)-were found to induce a changed response to antibiotics. Killing curves in the presence and absence of sublethal herbicide concentrations showed that the directions and the magnitudes of responses varied by herbicide, antibiotic, and species. When induced, MICs of antibiotics of five different classes changed up to 6-fold. In some cases the MIC increased, and in others it decreased. Herbicide concentrations needed to invoke the maximal response were above current food maximum residue levels but within application levels for all herbicides. Compounds that could cause induction had additive effects in combination. The role of soxS, an inducer of the AcrAB efflux pump, was tested in β-galactosidase assays with soxS-lacZ fusion strains of E. coli. Dicamba was a moderate inducer of the sox regulon. Growth assays with Phe-Arg β-naphtylamide (PAβN), an efflux pump inhibitor, confirmed a significant role of efflux in the increased tolerance of E. coli to chloramphenicol in the presence of dicamba and to kanamycin in the presence of glyphosate. Pathways of exposure with relevance to the health of humans, domestic animals, and critical insects are discussed. IMPORTANCE: Increasingly common chemicals used in agriculture, domestic gardens, and public places can induce a multiple-antibiotic resistance phenotype in potential pathogens. The effect occurs upon simultaneous exposure to antibiotics and is faster than the lethal effect of antibiotics. The magnitude of the induced response may undermine antibiotic therapy and substantially increase the probability of spontaneous mutation to higher levels of resistance. The combination of high use of both herbicides and antibiotics in proximity to farm animals and important insects, such as honeybees, might also compromise their therapeutic effects and drive greater use of antibiotics. To address the crisis of antibiotic resistance requires broadening our view of environmental contributors to the evolution of resistance.