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Antimicrobial Agents and Chemotherapy, May 2007, p. 1678-1686, Vol. 51, No. 5
0066-4804/07/$08.00+0     doi:10.1128/AAC.01411-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Effect of Macrolide Usage on Emergence of Erythromycin-Resistant Campylobacter Isolates in Chickens

Jun Lin,^1, Meiguan Yan,^2, Orhan Sahin,² Sonia Pereira,² Yun-Juan Chang,¹ and Qijing Zhang^2*

Department of Animal Science, University of Tennessee, Knoxville, Tennessee 37996,¹ Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, Iowa 50011²

Received 11 November 2006/ Returned for modification 27 December 2006/ Accepted 2 March 2007

In this work we conducted both in vitro and in vivo experiments to examine the development and mechanisms of erythromycin (Ery) resistance in Campylobacter jejuni and Campylobacter coli. In vitro plating revealed that both Campylobacter species had similar but low spontaneous mutation frequencies (3 x 10^–9 to <5.41 x 10^–10) for Ery resistance. Chickens infected with C. jejuni or C. coli were subjected to single or multiple treatments with medicated water containing tylosin (0.53 g/liter), which transiently reduced the level of Campylobacter colonization but did not select for Ery-resistant (Ery^r) mutants in the treated birds. However, when tylosin was given to the chickens in feed at a growth-promoting dose (0.05 g/kg feed), Ery^r mutants emerged in the birds after prolonged exposure to the antibiotic. The vast majority of the in vitro- and in vivo-selected Campylobacter mutants with Ery MICs of 8 to 256 µg/ml lacked the known resistance-associated mutations in the 23S rRNA gene, while the highly resistant mutants (Ery MIC > 512 µg/ml) had the A2074G mutation in the 23S rRNA gene. Inactivation of CmeABC, a multidrug efflux pump, dramatically reduced the Ery MIC in all of the examined mutants regardless of the presence of the A2074G mutation. Together, these results reveal distinct features associated with Ery resistance development in Campylobacter, demonstrate the significant role of CmeABC in Ery resistance, and suggest that long-term use of a macrolide as a growth promoter selects for the emergence of Ery^r Campylobacter in animal reservoirs.

Published ahead of print on 12 March 2007.

These authors contributed equally to this work.

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