Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2000
Publication Date: 12/1/2000
Citation: White, D.G., Jackson, C.R., Maurer, J.J., Ayers, S., Zhao, S., Lee, M.D., Bolton, L., Foley, T., Sherwood, J. 2000. Characterization of chloramphenicol and florefenicol resistance in escherichia coli associated with bovine diarrhea. Journal of Clinical Microbiology. Vol. 38. No. 12. P. 4593-4598. Interpretive Summary: Antimicrobial resistance is a major health concern in both human and veterinary medicine. Because of the growing concern of the failure of antimicrobials in disease treatment, resistance to antimicrobials in bacteria such as E. coli is being intensely studied. In this investigation, resistance of E. coli to the antimicrobial, florfenicol, in cattle with diarrhea was determined. Eighty-five percent (41/48) isolates were resistant to florfenicol and chloramphenicol. These E.coli isolates were resistant to florfenicol mediated by the flo gene, which specifies nonenzymatic cross-resistance to both florfenicol and chloramphenicol. Its presence among bovine E. coli isolates of diverse genetic backgrounds indicates a distribution much wider than previously thought. Scientists and veterinarians will use this information to further understand the patterns of antimicrobial resistance in the animal l population. This study will be useful in the disease treatment of farm animals.
Technical Abstract: Florfenicol, a veterinary fluorinated analog of thiamphenicol, is approved for treatment of bovine respiratory pathogens in the United States. However, florfenicol resistance has recently emerged among veterinary Escherichia coli isolates incriminated in bovine diarrhea. The flo gene, which confers resistance to florfenicol and chloramphenicol, has previously been identified in Photobacterium piscicida and Salmonell enterica serovar Typhimurium DT104. Forty-eight E. coli isolates recovered from calves with diarrhea, including 41 that were both chloramphenicol and florfenicol resistant, were assayed for the presence of both flo and cmlA genes. Forty-two of the 44 isolates for which florfenicol MICs were >16 ug/ml were positive via PCR for the flo gene. All E. coli isolates for which florfenicol MICs were <8 ug/ml were negative for the flo gene. Twelve E. coli isolates were positive for cmlA, and chloramphenicol MICs for all 12 were >32 ug/ml. Additionally, eight isolates were positive for both flo and cmlA, and both florfenicol and chloramphenicol MICs for these isolates were >64 ug/ml. The flo gene was identified on high-molecular-weight plasmids of approximately 225 kb among the majority of florfenicol-resistant E. coli isolates. However, not all of the florfenicol-resistant E. coli isolates tested contained the large flo-positive plasmids. This suggests that several of the E. coli isolates may possess a chromosomal flo gene.