Cross-resistance between triclosan and antibiotics in Pseudomonas aeruginosa is mediated by multidrug efflux pumps: Exposure of a susceptible mutant strain to triclosan selects nfxB mutants overexpressing MexCD-OprJ

Triclosan is an antiseptic frequently added to items as diverse as soaps, l otions, toothpaste, and many commonly used household fabrics and plastics. Although wild-type Pseudomonas aeruginosa expresses the triclosan target en oyl-acyl carrier protein reductase, it is triclosan resistant due to expres sion of the MexAB-OprM efflux system. Exposure of a susceptible Delta (mexA B-oprM) strain to triclosan selected multidrug-resistant bacteria at high f requencies. These bacteria hyperexpressed the MexCD-OprJ efflux system due to mutations in its regulatory gene, nfxB. The MICs of several drugs for th ese mutants were increased up to 500-fold, including the MIC of ciprofloxac in, which was increased 94-fold. Whereas the MexEF-OprN efflux system also participated in triclosan efflux, this antimicrobial was not a substrate fo r MexXY-OprM.