JAC Advance Access published online on May 7, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn190
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Original research |
Persistence of Campylobacter species, strain types, antibiotic resistance and mechanisms of tetracycline resistance in poultry flocks treated with chlortetracycline
1 Antimicrobial Agents Research Group, Division of Immunity and Infection, The Medical School, University of Birmingham, Birmingham, UK 2 Health Protection Agency Foodborne Zoonoses Unit, School of Clinical Veterinary Science, University of Bristol, Bristol, UK 3 Centre for Infections, Health Protection Agency, London, UK 4 Foodborne Zoonoses Group, School of Clinical Veterinary Science, University of Bristol, Bristol, UK
Received 20 December 2007; returned 5 February 2008; revised 20 March 2008; accepted 4 April 2008
* Corresponding author. Tel: +44-121-414-6966; Fax: +44-121-414-6819; E-mail: l.j.v.piddock{at}bham.ac.uk
Objectives: The aim of this study was to investigate the persistence of Campylobacter species, strain types, antibiotic resistance and mechanisms of tetracycline resistance in poultry flocks treated with chlortetracycline.
Methods: Three commercially reared broiler flocks, naturally colonized with Campylobacter, were treated with chlortetracycline under experimental conditions. The numbers of Campylobacter isolated, and the species, flaA short variable region allele, and antimicrobial resistance of isolates were determined.
Results: For two of three flocks, tetracycline-resistant strains predominated prior to chlortetracycline exposure. Presence of the antibiotic had no discernible effect on the numbers or types of Campylobacter and the tetracycline-resistant strains persisted in numbers similar to those observed before treatment. With all flocks, some faecal samples were obtained that contained no Campylobacter, irrespective of exposure to chlortetracycline; this was more common as the birds grew older. For the third flock, tetracycline-resistant Campylobacter were in the minority of samples before and during exposure to chlortetracycline, but at sampling times after this, no resistant strains were found in the treated (or untreated) birds, irrespective of exposure to the antibiotic. All tetracycline-resistant isolates (MICs 16 to >128 mg/L) contained tet(O) and, for some isolates, this was transferable to Campylobacter jejuni 81116. The efflux pump inhibitor PAβN reduced the MICs of tetracycline for these isolates by 4-fold, suggesting that an intact efflux pump, presumably CmeABC, is required for high-level tetracycline resistance.
Conclusions: Our data indicate that chlortetracycline treatment does not eradicate tetracycline-resistant Campylobacter spp. from poultry. However, if a low number of resistant isolates are present, then the antibiotic pressure appears insufficient to select such strains as the dominant population.
Key Words: chickens , typing , tetracycline-resistant
Present address. Health Protection Agency Yorkshire and the Humber, Leeds, UK.
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