Genotypic characterization of Salmonella enteritidis phage types by plasmid analysis, ribotyping, and pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was used to resolve XbaI and SpeI macrorestriction fragments from 60 defined phage type (PT) reference strains of Salmonella enteritidis. The level of discrimination was compared to that afforded by plasmid profile analysis and ribotyping. Twenty-eight distinct XbaI pulsed-field profiles (PFPs) were observed, although a single type, PFP X1, predominated. Absence of the 57-kb spy-associated fragment was observed for three PT reference strains, and the profile was designated PFP X1A. The;XbaI macrorestriction profiles of a further four PT reference strains were altered by the presence of plasmid-associated bands. Twenty-six SpeI-generated PFPs (plus one subtype) were observed for the same strains. No SpeI fragment corresponding to the 38-MDa serovar-specific plasmid was detected. The distribution of XbaI and SpeI profiles did not always correspond, producing a total of 32 combined PFPs for the 60 PT reference strains. This compared with a total of 18 different plasmid profiles and three PvuII ribotypes generated by the same strains. The results of this study indicate that PFGE may offer an improved level of discrimination over other genotypic typing methods for the epidemiological typing of S. enteritidis.