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

Campylobacter is a bacterial pathogen that causes human foodborne illnesses worldwide, and outbreaks have been associated with consumption of undercooked chicken livers. The objectives of this study were to compare two PCR assays of 250 Campylobacter isolates for identification to species, to assess antibiotic resistance of the isolates, and to analyze genetic diversity of the quinolone resistance determining regions (QRDRs) of the isolates. A double-blind design was used to identify the species of Campylobacter; 181 (72%) of the 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 resistant to at least one antibiotic. Among 88 C. jejuni isolates, 33 (18%) were resistant to nalidixic acid (NAL) and ciprofloxacin (CIP), 25 (14%) were resistant to tetracycline (TET), and 18 (10%) were resistant to NAL and TET. Two C. jejuni isolates were resistant to four of the tested antibiotics, and one isolate was resistant to five antibiotics. Two C. coli isolates were resistant to TET, and two were resistant to NAL, CIP, and TET. The amino acid sequences of the QRDRs for the isolates had 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 (substitution from threonine to isoleucine). However, six isolates without this substitution were resistant to NAL and/or CIP. Ten isolates with a point mutation at residue 86 were susceptible to NAL and CIP. This observation suggests that in addition to the substitution at residue 86 other mechanisms may confer resistance to quinolones. Further studies are needed to elucidate mechanisms for quinolone resistance in Campylobacter. The Campylobacter spp. isolated from chicken livers in this study were resistant to quinolones and other classes of antibiotics.

Automated summary

This study compared two PCR assays to identify Campylobacter isolates and evaluated their antibiotic resistance and genetic diversity of quinolone resistance determining regions (QRDRs). The findings showed that some isolates were resistant to antibiotics and had various mutations in the QRDRs. In addition to the mutation at residue 86, other mechanisms may contribute to quinolone resistance.