Journal Article

Effect of triclosan or a phenolic farm disinfectant on the selection of antibiotic-resistant <i>Salmonella enterica</i>

L. P. Randall, S. W. Cooles, L. J. V. Piddock and M. J. Woodward

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 54, issue 3, pages 621-627
Published in print September 2004 | ISSN: 0305-7453
Published online September 2004 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dkh376
Effect of triclosan or a phenolic farm disinfectant on the selection of antibiotic-resistant Salmonella enterica

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Objective: To determine the effect of growth of five strains of Salmonella enterica and their isogenic multiply antibiotic-resistant (MAR) derivatives with a phenolic farm disinfectant or triclosan (biocides) upon the frequency of mutation to resistance to antibiotics or cyclohexane.

Methods: Strains were grown in broth with or without the biocides and then spread on to agar containing ampicillin, ciprofloxacin or tetracycline each at 4× MIC or agar overlaid with cyclohexane. Incubation was for 24 and 48 h and the frequency of mutation to resistance was calculated for strains with and without prior growth with the biocides. MICs were determined and the presence of mutations in the acrR and marR regions was determined by sequencing and the presence of mutations in gyrA by light-cycler analysis, for a selection of the mutants that arose.

Results: The mean frequency of mutation to antibiotic or cyclohexane resistance was increased ∼10- to 100-fold by prior growth with the phenolic disinfectant or triclosan. The increases were statistically significant for all antibiotics and cyclohexane following exposure to the phenolic disinfectant (P ≤ 0.013), and for ampicillin and cyclohexane following exposure to triclosan (P ≤ 0.009). Mutants inhibited by >1 mg/L ciprofloxacin arose only from strains that were MAR. Reduced susceptibility to ciprofloxacin (at 4× MIC for parent strains) alone was associated with mutations in gyrA. MAR mutants did not contain mutations in the acrR or marR region.

Conclusions: These data renew fears that the use of biocides may lead to an increased selective pressure towards antibiotic resistance.

Keywords: ciprofloxacin; efflux; cyclohexane; MAR; gyrA

Journal Article.  4864 words. 

Subjects: Medical Oncology ; Critical Care

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