JAC Advance Access originally published online on May 23, 2005
Journal of Antimicrobial Chemotherapy 2005 56(1):216-219; doi:10.1093/jac/dki161
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Published by Oxford University Press 2005.
Identification of antimicrobial resistance and class 1 integrons in Shiga toxin-producing Escherichia coli recovered from humans and food animals
1 Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food & Drug Administration, 8401 Muirkirk Road, Laurel, MD 20708, USA; 2 Department of Nutrition and Food Science, University of Maryland, College Park, MD, USA; 3 Gastroenteric Disease Center, The Pennsylvania State University, University Park, PA, USA
Received 6 January 2005; returned 8 February 2005; revised 15 April 2005; accepted 17 April 2005
*Corresponding author. Tel: +1-301-827-8139; Fax: +1-301-827-8127; Email: szhao{at}cvm.fda.gov
Objectives: The objective of this study was to identify antimicrobial resistance and class 1 integrons among Shiga toxin-producing Escherichia coli (STEC).
Methods: Two-hundred and seventy-four STEC recovered from poultry, cattle, swine and humans were characterized by antimicrobial susceptibility testing, screened for the presence of class 1 integrons by PCR, and assayed for integron transfer by conjugation.
Results: Ninety-three (34%) of the isolates were resistant to streptomycin, followed by 89 (32%) to sulfamethoxazole, 83 (30%) to tetracycline, 48 (18%) to ampicillin, 29 (11%) to cefalothin, 22 (8%) to trimethoprim/sulfamethoxazole, 18 (7%) to gentamicin, 13 (5%) to chloramphenicol and 10 (4%) to cefoxitin. Class 1 integrons were detected in 43 (16%) of the 274 isolates. The adenyl acetyltransferase gene, aadA, which confers resistance to streptomycin, was identified in integrons from 41 (95%) of these 43 isolates, and the dfrA12 gene, which confers resistance to trimethoprim, was identified in integrons from eight (19%) of the isolates. The sat1 gene, which confers resistance to streptothricin, an antimicrobial that has never been approved for use in the United States, was identified in integrons from three (7%) of the isolates. Transfer of integrons by conjugation between strains of E. coli resulted in transfer of antimicrobial-resistant phenotypes for ampicillin, chloramphenicol, cefalothin, gentamicin, tetracycline, trimethoprim, sulfamethoxazole and streptomycin.
Conclusions: Antimicrobial resistance is common in STEC. Class 1 integrons located on mobile plasmids have facilitated the emergence and dissemination of antimicrobial resistance among STEC in humans and food animals.
Keywords: gene cassettes , food-borne pathogens , STEC
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