title: Role of coresistance in the development of resistance to chloramphenicol in Escherichia coli isolated from sick cattle and pigs.
abstract: OBJECTIVE
  To determine the cause of persistent resistance to chloramphenicol (CP) after the ban on its use in food-producing animals in several countries.
  
  
  METHODS
  71 CP-resistant and 104 CP-susceptible Escherichia coli strains isolated from sick cattle and pigs in Japan.
  
  
  METHODS
  Susceptibility of all bacterial strains to thiamphenicol (TP) and florfenicol (FFC) was tested by use of an agar dilution method. The CP-resistance genes and variable region within class 1 integrons in CP-resistant strains were identified by use of a PCR assay.
  
  
  RESULTS
  The CP acetyltransferase gene (ie, cat1) was identified as the predominant CP-resistance gene in strains isolated from cattle, and the cat1and nonenzymatic CP-resistance gene (ie, cmlA) were the predominant CP-resistance genes in strains isolated from pigs. Additionally, strains with cat1 isolated from cattle often were resistant to ampicillin, dihydrostreptomycin (DSM), oxytetracycline, and trimethoprim (TMP), whereas strains with cat1 or cmlA isolated from pigs often were resistant to DSM and TMP. Class 1 integrons were significantly more prevalent in strains with CP-resistance genes, compared with prevalence in strains without CP-resistance genes. All gene cassettes within the integrons were involved in resistance to DSM, TMP, or both.
  
  
  CONCLUSIONS
  Coresistance that develops because of the use of DSM and TMP in cattle and pigs apparently contributes to the selection of CP-resistant strains of E coli. Thus, it is possible that bacterial resistance to CP in animals would persist despite a ban on the use of CP in cattle and pigs.
authors.affiliation: National Veterinary Assay Laboratory, Ministry of Agriculture, Forestry and Fisheries, 1-15-1 Tokura, Kokubunji, Tokyo 185-8511, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Harada
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asai
authors.forename: Akemi
authors.initials: A
authors.lastname: Kojima
authors.forename: Kanako
authors.initials: K
authors.lastname: Ishihara
authors.forename: Toshio
authors.initials: T
authors.lastname: Takahashi
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D002701:Chloramphenicol / Q000494:pharmacology*; D002702:Chloramphenicol Resistance / Q000235:genetics / Q000502:physiology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D032023:Integrons; D007564:Japan / Q000453:epidemiology; D007880:Legislation, Drug; D008826:Microbial Sensitivity Tests; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D002701:Chloramphenicol