Relative contribution of target gene mutation and efflux to fluoroquinolone and erythromycin resistance, in French poultry and pig isolates of Campylobacter coli.

Thirty-eight avian and swine French isolates of Campylobacter coli were studied for their mechanisms of co-resistance to fluoroquinolones and erythromycin. A Thr86Ile modification of GyrA, responsible for fluoroquinolone resistance, was found in all the strains. Two different levels of resistance to erythromycin (MIC of 8-16 or >/=256 mg/l) were observed. A A2075G mutation in the 23S rRNA genes was found only in the highly-resistant strains. Phe-Arg-beta-naphthylamide, an efflux pump inhibitor, potentiated erythromycin in all the strains examined but restored susceptibility only in the strains with a low-level of resistance. This suggests the involvement of efflux in intrinsic and in acquired low-level of resistance to erythromycin in C. coli.