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U.S. Department of Health and Human Services

Animal & Veterinary

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IDENTIFICATION AND EXPRESSION OF CEPHAMYCINASE BLA CMY GENES IN ESCHERICHIA COLI AND SALMONELLA ISOLATED FROM FOOD ANIMALS AND GROUND MEATS

FDA Veterinarian Newsletter September/October 2001 Volume XVI, No V

Summary

The emergence of bacterial resistance to antimicrobial agents is a worldwide problem that has been associated with inappropriate use of these agents in human and veterinary medicine. Recently, plasmid-mediated b-lactamases with extended resistance spectra, such as cephamycinase (CMY), have emerged. In this study, 60 E. coli and 21 Salmonella isolates, recovered from diseased cattle, poultry, swine and retail meats, that exhibited decreased susceptibilities to ceftiofur and/or ceftriaxone were examined for the presence of blaCMY genes using a PCR assay. PCR analysis revealed that 54 (90%) of the E. coli isolates and all 21 Salmonella possessed a blaCMY gene. DNA sequence analysis of nine blaCMY PCR products (four from E. coli and five from Salmonella) indicated 95 to 99% homology to previously reported blaCMY-2 genes found in Klebsiella pneumonia and Salmonella Seftenberg. The blaCMY gene from an E. coli strain isolated from retail chicken meat was successfully transferred via conjugation. Transconjugants demonstrated resistance to six b-lactams drugs tested, including ceftiofur, ceftriaxone, cefoxitin, cephalothin, ampicillin and amoxicillin/clavulanic acid. This blaCMY gene was subsequently cloned into expression vector pET34b+ and transformed into E. coli BL21(DE3)pLysS. The transformant displayed resistance to ceftiofur, cepholothin, ampicillin and amoxicillin/clavulanic acid, and decreased susceptibilities to ceftriaxone, and cefoxitin. The cloned E. coli blaCMY gene sequence was 100% homologous to a previously reported blaCMY-4 gene of an E. coli strain isolated from leukemia patients. Our results indicate that blaCMY genes are commonly present in ceftiofur- and/or ceftriaxone-resistant E. coli and Salmonella of animal and food origin, and that this plasmid-mediated resistance is transferable via conjugation.