title: Identification of a novel G2073A mutation in 23S rRNA in amphenicol-selected mutants of Campylobacter jejuni.
abstract: OBJECTIVE
  This study was conducted to examine the development and molecular mechanisms of amphenicol resistance in Campylobacter jejuni by using in vitro selection with chloramphenicol and florfenicol. The impact of the resistance development on growth rates was also determined using in vitro culture.
  
  
  METHODS
  Chloramphenicol and florfenicol were used as selection agents to perform in vitro stepwise selection. Mutants resistant to the selective agents were obtained from the selection process. The mutant strains were compared with the parent strain for changes in MICs and growth rates. The 23S rRNA gene and the L4 and L22 ribosomal protein genes in the mutant strains and the parent strain were amplified and sequenced to identify potential resistance-associated mutations.
  
  
  RESULTS
  C. jejuni strains that were highly resistant to chloramphenicol and florfenicol were obtained from in vitro selection. A novel G2073A mutation in all three copies of the 23S rRNA gene was identified in all the resistant mutants examined, which showed resistance to both chloramphenicol and florfenicol. In addition, all the mutants selected by chloramphenicol also exhibited the G74D modification in ribosomal protein L4, which was previously shown to confer a low-level erythromycin resistance in Campylobacter species. The mutants selected by florfenicol did not have the G74D mutation in L4. Notably, the amphenicol-resistant mutants also exhibited reduced susceptibility to erythromycin, suggesting that the selection resulted in cross resistance to macrolides.
  
  
  CONCLUSIONS
  This study identifies a novel point mutation (G2073A) in 23S rRNA in amphenicol-selected mutants of C. jejuni. Development of amphenicol resistance in Campylobacter likely incurs a fitness cost as the mutant strains showed slower growth rates in antibiotic-free media.
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Licai
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Zhangqi
authors.initials: Z
authors.lastname: Shen
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Gaowa
authors.initials: G
authors.lastname: Naren
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Xi
authors.initials: X
authors.lastname: Xia
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Congming
authors.initials: C
authors.lastname: Wu
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Shen
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Development and Evaluation of Chemical and Herbal Drugs for Animal Use, College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D016123:Campylobacter jejuni / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D002701:Chloramphenicol / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D007700:Kinetics; D009154:Mutation / Q000235:genetics*; D012338:RNA, Ribosomal, 23S / Q000235:genetics*; D013839:Thiamphenicol / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D012338:RNA, Ribosomal, 23S; D002701:Chloramphenicol; C035534:florfenicol; D013839:Thiamphenicol
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