MexAB-OprM Efflux Pump of Offers Resistance to Carvacrol: A Herbal Antimicrobial Agent.

Carvacrol is a herbal antimicrobial agent with activity against several bacterial pathogens. However, multidrug resistant strains of are resistant to herbal antimicrobial compounds including carvacrol. Resistance of to carvacrol is not well studied. This study was aimed to identify the gene(s) associated with carvacrol resistance, thus to understand its mechanisms in . A herbal drug resistant strain was isolated from a hospital environment. Carvacrol sensitive mutant was generated using transposon mutagenesis. The inactivated gene in the mutant was identified as , which is part of the operon. Inactivation of the gene resulted in a >31-fold reduction in MIC of carvacrol, whereas a >80-fold reduction was observed in the presence of drug efflux inhibitor phenylalanine-arginine β-naphthylamide (PAβN). The parental herbal-resistant strain was completely killed within 3 h of incubation in the presence of carvacrol and PAβN. The inactivation did not affect the resistance to other herbal compounds used. The results demonstrate that resistance to carvacrol in is mediated by the MexABOprM efflux pump.