Prevalence and Characterization of Quinolone Resistance in Campylobacter spp. Isolates in Chicken Livers from Retail Stores in Georgia, USA

Abstract

Campylobacter is the leading bacterial pathogen that causes human foodborne illnesses worldwide and outbreaks have been associated with consumption of under-cooked chicken livers.  The objectives of this study were to compare two PCR assays for speciation of 250 Campylobacter isolates, to assess antibiotic resistance of the isolates, and to analyze genetic diversity of the quinolone resistance determining regions (QRDR) of the isolates.  Speciation was performed in a double-blind manner, and results showed that 181 (72%) isolates were identified as Campylobacter jejuni and 69 (28%) isolates were identified as Campylobacter coli by both PCR assays.  A total of 93 (37.2%) isolates were determined to be resistant to at least one antibiotic.  Among 88 C. jejuni isolates, 33 isolates (18%) were resistant to nalidixic acid (NAL) and ciprofloxacin (CIP), followed by 25 (14%) isolates resistant to tetracycline (TET) and 18 (10%) isolates resistant to NAL and TET.  Two isolates were resistant to four antibiotics tested.  One isolate was resistant to five antibiotics tested.  For C. coli, two isolates were resistant to TET, and two were resistant to NAL, CIP and TET.  The amino acid sequences of the QRDR regions among the isolates revealed eight point mutations and could be classified into 12 groups. Thirty-eight C. jejuni isolates resistant to NAL and CIP had a point mutation at residue 86 (Thr to Ile substitution). However, six isolates without the substitution at the same position were resistant to NAL and/or CIP.  In addition, 10 isolates with a point mutation at residue 86 were susceptible to NAL and CIP.  This observation suggests that besides the substitution at 86, other mechanisms may confer resistance to quinolones.  Further studies are needed to elucidate mechanisms for quinolone resistance in Campylobacter.  Based on our results, the Campylobacter spp. isolated from chicken livers were found to be resistant to the quinolones and other classes of antibiotics.