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

colonization of Campylobacter jejuni J. Lin & M. Ensminger Department of Animal Science, The University of Tennessee, Knoxville, TN Summary CmeABC, a multidrug efflux pump, contributes to Campylobacter resistance to a broad spectrum of antimicrobial agents and is also essential for Campylobacter colonization by mediation of bile resistance. We hypothesize that inhibition of CmeABC will not only control antibiotic resitance but also increase the susceptibility of Campylobacter to in vivo bile salts, consequently decreasing the colonization level of Campylobacter in poultry. Using both in vitro and in vivo systems, we examined the effect of efflux pump inhibitors (EPIs) on the susceptibility of Campylobacter to various antimicrobials. Presence of the EPI resulted in 2to 2048-fold reduction in the MICs of antimicrobials known to be substrates of CmeABC pump in all Campylobacter strains. Particularly, the MICs of selected bile salts were dramatically decreased 64to 512-fold when the EPI was used. The intrinsic and acquired resistance of C. jejuni to macrolide was decreased significantly (32to 64-fold reduction in the MIC of erythromycin) in the presence of the EPI. Investigation of 57 clinical Campylobacter isolates of various origins further showed that the EPI decreased the MICs of erythromycin (2to 512-fold) in all isolates. The inhibitory effect of the EPI was does-dependents and as low as 0.5 μg/ml of the EPI resulted in decreased MIC of antimicrobials in C. jejuni. Presence of the EPI decreased the frequency of emergence of erythromycin-resistant mutants in C. jejuni (<10), which is well below normal frequency of approximate 10. Notably, MIC of erythromycin was also greatly decreased (> 4-fold) in CmeB mutants in the presence of EPI, suggesting the existence of other pump(s) involved in macrolide resistance in C. jejuni. Chicken colonization study demonstrated