Relative contribution of target gene mutation and efflux to varying quinolone resistance in Irish Campylobacter isolates

The contribution of target gene mutations and active efflux to varying levels of quinolone resistance in Irish Campylobacter isolates was studied. The Thr-86-Ile modification of GyrA did not correlate with the level of quinolone resistance. The efflux pump inhibitor Phe-Arg-β-Naphthylamide (PAβN) had no effect on the MICs to ciprofloxacin. In contrast, a PAβN sensitive efflux system contributed to the low-level nalixidic acid resistance phenotype. The lack of effect of PAβN in high-level resistant nalidixic isolates may be attributable to mutations identified in the CmeB efflux pump of these isolates. PAβN may have limited diagnostic value in the assessment of the contribution of efflux pump activity to ciprofloxacin resistance in Campylobacter.