A phenylalanine-arginine beta-naphthylamide sensitive multidrug efflux pump involved in intrinsic and acquired resistance of Campylobacter to macrolides.

The macrolide erythromycin is the antibiotic of choice in the management of Campylobacter infections. Although mutation has been reported to account for resistance to the antibiotic, resistance may also be due to an efflux pump that extrudes the drug prior to reaching its target. Moreover, the efflux pump may be one that accommodates resistance to other related or unrelated drugs (multidrug resistance). We examined the possibility that resistance to erythromycin may involve an efflux pump whose presence may be identified by the use of the unique commercial inhibitor of the previously described efflux pumps phenylalanine-arginine beta-naphtylamide (PAbetaN). We showed that PAbetaN is able to significantly increase the susceptibility of the reference strain NCTC 11168 to erythromycin, suggesting that an efflux pump functions at a basal level in the reference wild type strain. Erythromycin-resistant isolates were tested for their response to PAbetaN treatment. Among the strains tested, resistance of three isolates to erythromycin was reduced to a level comparable to that of the susceptible strain when the strains were grown in the presence of this inhibitor. To conclude, besides mutations, erythromycin resistance in Campylobacter may also be due to an efflux mechanism sensitive to PAbetaN.