Evolution of chloramphenicol resistance, with emergence of cross-resistance to florfenicol, in bovine Salmonella Typhimurium strains implicates definitive phage type (DT) 104

J Med Microbiol. 2000 Jan;49(1):103-110. doi: 10.1099/0022-1317-49-1-103.


The prevalence of resistance to florfenicol, a phenicol drug newly introduced in veterinary therapy, was determined in 86 chloramphenicol-resistant Salmonella Typhimurium isolates from cattle collected during 1985-1995. All were highly resistant to chloramphenicol (MICs > or = 128 mg/L) and 38 were simultaneously resistant to florfenicol (MICs >16 mg/L) and to beta-lactam agents, spectinomycin, streptomycin, sulphonamides and tetracyclines. The isolates susceptible to florfenicol harboured the chloramphenicol acetyl transferase gene, cat of type I. All the florfenicol-resistant isolates harboured the floR resistance gene and the characteristic multiple resistance genetic locus, previously characterised in a S. Typhimurium DT104 strain and identified by a multiplex PCR. Plasmid profiles and ribotype patterns were determined for all the isolates. The florfenicol-resistant isolates were grouped into the same ribotyping pattern and presented similar plasmid profiles, whereas the florfenicol-susceptible isolates showed a wider genetic diversity that is usual for S. Typhimurium. Thus, the florfenicol-resistant isolates could represent a clonal cluster, closely related to, if not of DT104 phage type, which appeared in 1989 and is now predominant within chloramphenicol-resistant S. Typhimurium. The multiplex PCR provided a useful tool to survey further evolution of multiresistant S. Typhimurium strains.

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Bacteriophage Typing / veterinary
  • Cattle
  • Cattle Diseases / microbiology
  • Chloramphenicol Resistance* / genetics
  • DNA, Bacterial / analysis
  • DNA, Ribosomal / analysis
  • Drug Resistance, Microbial / genetics
  • Drug Resistance, Multiple / genetics
  • Lactams
  • Microbial Sensitivity Tests / veterinary
  • R Factors
  • Retrospective Studies
  • Salmonella Infections, Animal / microbiology
  • Salmonella typhimurium / classification
  • Salmonella typhimurium / drug effects*
  • Salmonella typhimurium / genetics
  • Spectinomycin / pharmacology
  • Streptomycin / pharmacology
  • Sulfonamides / pharmacology
  • Tetracyclines
  • Thiamphenicol / analogs & derivatives*
  • Thiamphenicol / pharmacology


  • Anti-Bacterial Agents
  • DNA, Bacterial
  • DNA, Ribosomal
  • Lactams
  • Sulfonamides
  • Tetracyclines
  • Spectinomycin
  • florfenicol
  • Thiamphenicol
  • Streptomycin