Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 4, 2005
Publication Date: April 20, 2006
Citation: Jesse, T.W., Englen, M.D., Pittenger, L.G., Cray, P.J. 2006. Two distinct mutations in gyra lead to ciprofloxacin and nalidixic acid resistance in campylobacter coli and campylobacter jejuni isolated from chickens and beef cattle. Journal of Applied Microbiology. 100(4):682-688. Interpretive Summary: Campylobacter is the most common cause of acute bacterial diarrhea in humans worldwide. The emergence of strains resistant to antimicrobials used to treat humans has become a major concern. The drug ciprofloxacin is frequently prescribed to treat Campylobacter infections. In this study, the molecular mechanisms that confer resistance in Campylobacter to ciprofloxacin and the related antimicrobial, nalidixic acid, were examined. Most of the strains resistant to both these drugs had specific mutations in a gene known as gyrA. The role of a recently described intracellular drug pump known as cmeB was also investigated but it did not appear to contribute significantly to the development of resistance. Resistant strains with an unknown mechanism of resistance were also identified. We conclude that resistance to nalidixic acid and ciprofloxacin can be conferred by multiple mechanisms. This work provides valuable new information on the mechanisms of antimicrobial resistance in a major bacterial pathogen. It will be useful to producers, regulatory agencies, and researchers studying antimicrobial resistance.
Technical Abstract: Aims:The aim of this study was to identify point mutations in the gyrA quinolone resistance determining region (QRDR) of Campylobacter coli and Campylobacter jejuni that confer nalidixic acid (NAL) resistance without conferring cross-resistance to ciprofloxacin (CIP). In addition, the role of cmeB in quinolone resistance was examined. Methods: Point mutations in the QRDR of gyrA from C. coli and C. jejuni isolates were identified by direct sequencing. The potential contribution of the Campylobacter multidrug efflux pump (CmeB) to CIP and NAL resistance in these isolates was determined by PCR for the cmeB gene. Results: All isolates with minimum inhibitory concentrations (MICs) greater than or equal to 4 µg/ml for CIP and greater than or equal to 32 µg/ml for NAL possessed a missense mutation leading to substitution of Ile for Thr at codon 86. Three isolates with a missense mutation leading to a Thr86Ala substitution had MICs < 4 µg/ml for CIP and greater than or equal to 32 µg/ml for NAL. Twelve isolates were PCR-negative for cmeB, indicating a lack of the cmeB gene. Five of the twelve isolates had MICs of greater than or equal to 4 µg/ml for CIP and greater than or equal to 32 µg/ml for NAL and had the Thr86Ile mutation; three were not resistant to CIP or NAL. The remaining four cmeB-negative isolates had MICs < 4 µg/ml for CIP and greater than or equal to 32 µg/ml for NAL. However, no gyrA mutations were detected. Conclusions: These data confirm that Thr86Ile mutations lead to ciprofloxacin and nalidixic acid cross-resistance. However, resistance to nalidixic acid alone was conferred by a single Thr86Ala mutation. The absence of cmeB did not affect nalidixic acid resistance in four of the isolates studied, suggesting that other mechanisms may play a role in quinolone resistance in Campylobacter.