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

• Published in: Journal of antimicrobial chemotherapy 2004-09, Vol.54 (3), p.621-627
• Main Authors: Randall, L. P., Cooles, S. W., Piddock, L. J. V., Woodward, M. J.
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Anti-Infective Agents, Local - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; Biological and medical sciences; Chemistry, Agricultural; ciprofloxacin; Ciprofloxacin - pharmacology; cyclohexane; Cyclohexanes - pharmacology; Disinfectants - pharmacology; DNA Gyrase - genetics; DNA Primers; Drug Resistance, Bacterial; efflux; gyrA; MAR; Medical sciences; Membrane Transport Proteins - genetics; Mutation - genetics; Mutation - physiology; Pharmacology. Drug treatments; Phenols - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; Salmonella; Salmonella enterica; Salmonella enterica - drug effects; Salmonella enterica - genetics; Salmonella enterica - growth & development; Triclosan - pharmacology
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkh376

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.