Effect of efflux pump inhibitors on bile resistance and in vivo colonization of Campylobacter jejuni

Objectives: The multidrug efflux pump CmeABC is essential for Campylobacter colonization in animal intestine by mediating bile resistance. The objective of this study is to examine the effect of inhibition of the CmeABC pump by efflux pump inhibitor (EPI) on the susceptibility of Campylobacter to bile salts and to evaluate the in vivo efficacy of two EPIs on the colonization of Campylobacter in a host. Methods: Two wild-type Campylobacter jejuni strains and their isogenic cmeB mutants were used to determine the susceptibilities of the strains to various bile salts in the presence of EPI MC-207,110 or MC-04,124. The in vivo effect of the EPIs on the colonization of C. jejuni in a host was evaluated using a chicken model system. Results: The presence of EPIs resulted in a 16- to 512-fold reduction in the MICs of bile salts in both C. jejuni strains. Compared with wild-type strains, cmeB mutants displayed much smaller magnitudes of reduction in the MICs of bile salts, indicating that the in vitro effect of the EPI is primarily mediated by the CmeABC efflux pump. Investigation of 21 Campylobacter isolates from various origins further showed that the EPI MC-207,110 decreased bile resistance in all isolates. Single oral administration of EPI (MC-207,110 or MC-04,124) at two different doses reduced colonization of C. jejuni in chickens at 2-4 days post-inoculation only. Oral administration of MC-207,110 for three consecutive days following inoculation of C. jejuni did not result in a more significant reduction in the level of Campylobacter colonization in chickens. Conclusions: Inhibition of Campylobacter efflux pumps by EPIs is a potential means for therapeutic intervention to reduce colonization of C. jejuni in humans and animal reservoirs.