rRNA gene restriction patterns and plasmid analysis as a tool for typing Salmonella enteritidis

We have evaluated the usefulness of ribosomal RNA gene restriction patterns and of plasmid analysis for the typing of Salmonella serotype enteritidis isolates. Strains were isolated from single patients excreting the organism for up to about 4 months, as well as from clusters of patients who had probably been exposed to the same source of infection. The sensitivity of ribosomal DNA (rDNA) analysis was dependent on the restriction enzyme used; of 14 different enzymes, only SmaI and SphI showed different rDNA patterns. Differences were detected between clusters, but all strains belonging to a given cluster showed identical rDNA patterns. In one single strain (isolated at day 66), we observed an SphI pattern that was not identical to that of the original isolate from the same patient. Strains were also typed by plasmid analysis. All strains harboured a plasmid of approximately 55 kb with identical restriction patterns. Smaller plasmids of 4.5 and 4.3 kb were isolated from all the strains belonging to one and two clusters, respectively. We have demonstrated that the analysis of rRNA genes is a sensitive and useful method for epidemiological typing of Salmonella serotype enteritidis, which can be complemented by analysis of plasmids if such structures are present.