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Applied and Environmental Microbiology, December 2006, p. 7813-7820, Vol. 72, No. 12
0099-2240/06/$08.00+0 doi:10.1128/AEM.01087-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Svetlana Kocherginskaya,2
Asma Mehboob,2
Matthew Robert,3
Roderick I. Mackie,2
Lutgarde Raskin,1,
and
Julie L. Zilles1*
Department of Civil and Environmental Engineering,1 Department of Animal Sciences,2 Department of Agricultural Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 618013
Received 11 May 2006/ Accepted 3 October 2006
Chlortetracycline and the macrolide tylosin were identified as commonly used antimicrobials for growth promotion and prophylaxis in swine production. Resistance to these antimicrobials was measured throughout the waste treatment processes at five swine farms by culture-based and molecular methods. Conventional farm samples had the highest levels of resistance with both culture-based and molecular methods and had similar levels of resistance despite differences in antimicrobial usage. The levels of resistance in organic farm samples, where no antimicrobials were used, were very low by a culture-based method targeting fecal streptococci. However, when the same samples were analyzed with a molecular method detecting methylation of a specific nucleotide in the 23S rRNA that results in resistance to macrolides, lincosamides, and streptogramin B (MLSB), an unexpectedly high level of resistant rRNA (approximately 50%) was observed, suggesting that the fecal streptococci were not an appropriate target group to evaluate resistance in the overall microbial community and that background levels of MLSB resistance may be substantial. All of the feed samples tested, including those from the organic farm, contained tetracycline resistance genes. Generally, the same tetracycline resistance genes and frequency of detection were found in the manure and lagoon samples for each commercial farm. The levels of tetracycline and MLSB resistance remained high throughout the waste treatment systems, suggesting that the potential impact of land application of treated wastes and waste treatment by-products on environmental levels of resistance should be investigated further.
Published ahead of print on 13 October 2006.
Present address: Carollo Engineers, Fountain Valley, CA 92708.
Present address: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109-2125.
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