Evolution and ecology of florfenicol antibiotic resistance
Keyes, Kathleen Fern
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The evolution of antibiotic resistance has become a ubiquitous problem in both human and veterinary medicine. Florfenicol, a veterinary fluorinated analogue of thiamphenicol and chloramphenicol, was approved in early 1996 for use in cattle for the treatment of infectious respiratory diseases that formerly responded to chloramphenicol. There is currently much interest in the potential use of florfenicol in industrial poultry farming. However, florfenicol resistance has already emerged in a number of veterinary bacterial isolates, including Escherichia coli and Salmonella enterica serovar Typhimurium DT104 in cattle. The gene flo, which confers resistance to florfenicol and chloramphenicol, has previously been identified in Photobacterium piscicida and Salmonella DT104. Resistance to florfenicol was detected in avian Escherichia coli isolates from clinical samples of sick chickens, although this antibiotic has as yet never been used in poultry. All florfenicol-resistant E. coli isolates were also positive for the florfenicol- resistance gene flo by polymerase chain reaction (PCR) screening. Molecular typing demonstrated that flo was independently acquired and is encoded on high-molecularweight plasmids. Two of the florfenicol-resistant isolates also contained intI1, the DNA integrase gene that is characteristic of Class 1 integrons, which are mobile transmissible elements deemed important in horizontal transfer of antibiotic resistance genes.