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FexA, a novel Staphylococcus lentus gene encoding resistance to florfenicol and chloramphenicol.

ABSTRACT: The Staphylococcus lentus plasmid pSCFS2 carries a novel florfenicol-chloramphenicol resistance gene, designated fexA, encoding a protein of 475 amino acids with 14 transmembrane domains. The FexA protein differs from all previously known proteins involved in the efflux of chloramphenicol and florfenicol. Induction of fexA expression by chloramphenicol and florfenicol occurs via translational attenuation.

SUBMITTER: Kehrenberg C

PROVIDER: S-EPMC321516 | biostudies-literature | 2004 Feb

REPOSITORIES: biostudies-literature

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fexA, a novel Staphylococcus lentus gene encoding resistance to florfenicol and chloramphenicol.

Kehrenberg Corinna C Schwarz Stefan S

Antimicrobial agents and chemotherapy 20040201 2

The Staphylococcus lentus plasmid pSCFS2 carries a novel florfenicol-chloramphenicol resistance gene, designated fexA, encoding a protein of 475 amino acids with 14 transmembrane domains. The FexA protein differs from all previously known proteins involved in the efflux of chloramphenicol and florfenicol. Induction of fexA expression by chloramphenicol and florfenicol occurs via translational attenuation. ...[more]

PMID: 14742219

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Project description:BackgroundWith the wide use of florfenicol to prevent and treat the bacterial infection of domestic animals, the emergence of the florfenicol resistance bacteria is increasingly serious. It is very important to elucidate the molecular mechanism of the bacteria's resistance to florfenicol.MethodsThe minimum inhibitory concentration (MIC) levels were determined by the agar dilution method, and polymerase chain reaction was conducted to analyze the distribution of florfenicol resistance genes in 39 CoNS strains isolated from poultry and livestock animals and seafood. The whole genome sequence of one multidrug resistant strain, Staphylococcus lentus H29, was characterized, and comparative genomics analysis of the resistance gene-related sequences was also performed.ResultsAs a result, the isolates from the animals showed a higher resistance rate (23/28, 82.1%) and much higher MIC levels to florfenicol than those from seafood. Twenty-seven animal isolates carried 37 florfenicol resistance genes (including 26 fexA, 6 cfr and 5 fexB genes) with one carrying a cfr gene, 16 each harboring a fexA gene, 5 with both a fexA gene and a fexB gene and the other 5 with both a fexA gene and a cfr gene. On the other hand, all 11 isolates from seafood were sensitive to florfenicol, and only 3 carried a fexA gene each. The whole genome sequence of S. lentus H29 was composed of a chromosome and two plasmids (pH29-46, pH29-26) and harbored 11 resistance genes, including 6 genes [cfr, fexA, ant(6)-Ia, aacA-aphD, mecA and mph(C)] encoded on the chromosome, 4 genes [cfr, fexA, aacA-aphD and tcaA] on pH29-46 and 1 gene (fosD) on pH29-26. We found that the S. lentus H29 genome carried two identical copies of the gene arrays of radC-tnpABC-hp-fexA (5671 bp) and IS256-cfr (2690 bp), of which one copy of the two gene arrays was encoded on plasmid pH29-46, while the other was encoded on the chromosome.ConclusionsThe current study revealed the wide distribution of florfenicol resistance genes (cfr, fexA and fexB) in animal bacteria, and to the best of our knowledge, this is the first report that one S. lentus strain carried two identical copies of florfenicol resistance-related gene arrays.

Project description: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 Salmonella enterica serovar Typhimurium DT104. The flo gene product is closely related to the CmlA protein identified in Pseudomonas aeruginosa. The cmlA gene confers nonenzymatic chloramphenicol resistance via an efflux mechanism. 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 > or =16 microg/ml were positive via PCR for the flo gene. All E. coli isolates for which florfenicol MICs were < or =8 microg/ml were negative for the flo gene (n = 4) Twelve E. coli isolates were positive for cmlA, and chloramphenicol MICs for all 12 were > or =32 microg/ml. Additionally, eight isolates were positive for both flo and cmlA, and both florfenicol and chloramphenicol MICs for these isolates were > or =64 microg/ml. DNA sequence analysis of the E. coli flo gene demonstrated 98% identity to the published GenBank sequences of both serovar Typhimurium flo(St) and P. piscicida pp-flo. 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. The E. coli flo gene specifies nonenzymatic cross-resistance to both florfenicol and chloramphenicol, and its presence among bovine E. coli isolates of diverse genetic backgrounds indicates a distribution much wider than previously thought.

Dataset Information

FexA, a novel Staphylococcus lentus gene encoding resistance to florfenicol and chloramphenicol.

Publications

fexA, a novel Staphylococcus lentus gene encoding resistance to florfenicol and chloramphenicol.

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