A novel phenicol exporter gene, fexB, found in enterococci of animal origin

Hebing Liu, Yang Wang, Congming Wu, Stefan Schwarz, Zhangqi Shen, Byeonghwa Jeon, Shuangyang Ding, Qijing Zhang, Jianzhong Shen

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Objectives: To investigate two porcine Enterococcus isolates for the genetic basis of phenicol resistance and to determine the location and the genetic environment of the novel resistance gene. Methods: A total of 391 isolates with reduced florfenicol susceptibility (MIC ≥16 mg/L), obtained from 557 nasal swabs of individual pigs, were screened by PCR for the known florfenicol resistance genes. Isolates that were negative in these PCRs were analysed for their species assignment and antimicrobial susceptibility. Plasmids were extracted and subjected to transformation and conjugation assays. Restriction fragments of the phenicol resistance plasmids were cloned and sequenced. The sequences obtained were analysed and compared with sequences deposited in the databases. Results: The two isolates, Enterococcus faecium EFM-1 and Enterococcus hirae EH-1, exhibited MICs of chloramphenicol and florfenicol of 64 mg/L and carried a new phenicol resistance gene, designated fexB. This gene codes for a phenicol exporter of 469 amino acids organized in 14 transmembrane domains. The fexB gene was located on the 35 kb pEFM-1 from E. faecium and on the 25.3 kb pEH-1 from E. hirae, respectively. Both plasmids were non-conjugative. The fexB gene was found to be embedded in virtually the same genetic environment of 14.8 kb in both plasmids. Conclusion: To the best of our knowledge, this is the first report of the new florfenicol exporter gene fexB. Based on its plasmid location, horizontal transfer from the enterococci to other bacteria is possible.

Original languageEnglish (US)
Article numberdkr481
Pages (from-to)322-325
Number of pages4
JournalJournal of Antimicrobial Chemotherapy
Issue number2
StatePublished - Feb 2012
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by the Chinese Universities Scientific Fund (15050102), National Natural Science Foundation of China (U1031004 and 31001087), and the Program for Chang Jiang Scholars and the Innovative Research Team at the University of China (IRT0866).


  • FexA
  • Florfenicol resistance
  • Food safety
  • Gram-positive bacteria


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