Continuous Exposure ofStaphylococcus epidermidisSE1457 to Triclosan Results in Marked Triclosan Resistance Due to a Mutation infabI

Triclosan is a multi-purpose biocide used in hundreds of personal care products, including but not limited to antibacterial hand soaps, lotions, and toothpastes. The ubiquitous usage of triclosan allows it to be widely dispersed into the environment, which could contribute to the resistance of environmental microorganisms to triclosan and perhaps to clinically relevant antibiotics. The aim of this study was to evaluate whether long-term exposure of the common skin bacterium, Staphylococcus epidermidis, to subinhibitory, but increasing concentrations of triclosan would select for triclosan-resistant mutants. The study began with exposure to 0.00015% triclosan, which was ten-fold less than the initial MIC. The concentration was increased with respect to observed increases in the MIC. The duration of the study led to the ability of the bacteria to grow in 0.15% triclosan. The fabI gene, the product of which is a known target of triclosan, was sequenced to determine whether the selection pressure applied by triclosan would induce mutations in this region of the genome. We found exposure of Staphylococcus epidermidis strain SE 1457 to increasing subinhibitory concentrations of triclosan for 70 days in broth cultures resulted in a notable increase in resistance to triclosan, and that these mutants contained a point mutation at position 284 in the fabI gene, leading a change at position 95 in enoyl-acyl carrier protein reductase.