Effects of two efflux pump inhibitors on the drug susceptibility of Riemerella anatipestifer isolates from China

The objective of this study was to verify the supposition that efflux might be involved in the drug resistance of Riemerella anatipestifer isolates. Two broad-spectrum efflux pump inhibitors, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and Phe-Arg-β-naphthylamide (PAβN), on the contribution of minimum inhibitory concentrations of amikacin, streptomycin, chloramphenicol, tetracycline, ceftriaxone, ceftazidime, nalidixic acid, levofloxacin, enrofloxacin, as well as ciprofloxacin against 69 clinical R. anatipestifer isolates were investigated. We first reported that the two efflux pump inhibitors could restore the antimicrobial susceptibility of R. anatipestifer isolates. It is suggested that active efflux system is possible to be linked with the development of resistance in R. anatipestifer isolates.