The distribution of serotype-specific plasmids among different subgroups of strains ofSalmonella entericaserotype Enteritidis: characterization of molecular variants by restriction enzyme fragmentation patterns

Abstract

SUMMARY: Four hundred and thirty-four isolates ofSalmonella entericaserotype Enteritidis were studied. They were grouped into five subsets defined by either the collection criteria or the parameter which formed the basis for subsequent analysis. Seventy-seven per cent harboured the serotype-specific plasmid (SSP). In 55% of the isolates this was the sole plasmid. Molecular variation in the SSP was detected in 17 (5%) of the isolates on the basis of restriction enzyme fragmentation pattern (REFP) analysis usingPstI andSmaI. The SSP variants were further characterized using additional restriction enzymes chosen to optimize the information content and analysed using a coefficient of similarity.A variant SSP designated pOG690 showed greater resemblance to the SSP ofSalmonella entericaserotype Typhimurium than Enteritidis; 89% and 68% respectively forPstI and 79% and 55% respectively forSmaI. In respect of thePstI data pOG690 shared at least 55 kb of DNA with the Typhimurium SSP and 37 kb with the SSP of Enteritidis. This variant was associated with poultry (duck, goose, chicken) and all isolates belonged to phage type 9b. Other variants were associated with phage types 4, 6, 6a, 9a, 11, 15 and 24. The epidemiological implications of these results are discussed.