Parallel evolutionary pathways to antibiotic resistance selected by biocide exposure

OBJECTIVES Biocides are widely used to prevent infection. We aimed to determine whether exposure of Salmonella to various biocides could act as a driver of antibiotic resistance. METHODS Salmonella enterica serovar Typhimurium was exposed to four biocides with differing modes of action. Antibiotic-resistant mutants were selected during exposure to all biocides and characterized phenotypically and genotypically to identify mechanisms of resistance. RESULTS All biocides tested selected MDR mutants with decreased antibiotic susceptibility; these occurred randomly throughout the experiments. Mutations that resulted in de-repression of the multidrug efflux pump AcrAB-TolC were seen in MDR mutants. A novel mutation in rpoA was also selected and contributed to the MDR phenotype. Other mutants were highly resistant to both quinolone antibiotics and the biocide triclosan. CONCLUSIONS This study shows that exposure of bacteria to biocides can select for antibiotic-resistant mutants and this is mediated by clinically relevant mechanisms of resistance prevalent in human pathogens.