Subtyping of Salmonella typhimurium by pulsed-field gel electrophoresis and comparisons with phage types and resistance types.

One-hundred and sixty-eight Salmonella enterica subsp. enterica serotype Typhimurium isolates have been analysed by phage typing, by pulsed-field gel electrophoresis and for their antimicrobial susceptibility. Those independent strains, isolated from food animal production including cattle, poultry and pig sectors have been collected by the French non human Salmonella network, during the first semester in 1999. Isolates encompassed 14 phage types. The majority of S. Typhimurium isolates was found to be definitive phage type DT104, representing 39% of all isolates. Other phage types were mainly DT8, PT U302, DT120, DT193 and DT135. Forty-six pulsotypes were obtained using Xbal restriction enzyme, and amongst them, ten were associated to the DT104 phage type. A major pulsotype (px1), was represented by 79% of DT104 isolates and was also found among DT120. Forty-eight percent of isolates showed a classic DT104 resistance profile to ampicillin, streptomycin, chloramphenicol, tetracycline, sulfonamides (ASCTSu). Among this resistance type, 84% were DT104 and 12% were DT120. Some pulsotypes were found associated to this resistant type. The pulsed field gel electrophoresis showed to be a useful typing method for discrimination of S. Typhimurium strains and for tracing clone through different sectors of origin in order to control their spread.