THE DISTRIBUTION OF SEROTYPE-SPECIFIC PLASMIDS AMONG DIFFERENT SUBGROUPS OF STRAINS OF SALMONELLA-ENTERICA SEROTYPE ENTERITIDIS - CHARACTERIZATION OF MOLECULAR VARIANTS BY RESTRICTION ENZYME FRAGMENTATION PATTERNS

Pour hundred and thirty-four isolates of Salmonella enterica serotype Enteritidis were studied. They were grouped into five subsets defined by either the collection criteria or the parameter which formed the ba sis for subsequent analysis. Seventy-seven per cent harboured the sero type-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 (RE FP) analysis using PstI and SmaI. The SSP variants were further charac terized using additional restriction enzymes chosen to optimize the in formation content and analysed using a coefficient of similarity. A va riant SSP designated pOG690 she-wed greater resemblance to the SSP of Salmonella enterica serotype Typhimurium than Enteritidis; 89% and 68% respectively for PstI and 79% and 55% respectively for SmaI. In respe ct-of the PstI data pOG690 shared at least 55 kb of DNA with the Typhi murium SSP and 37 kb with the SSP of Enteritidis. This variant was ass ociated 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 res ults are discussed.