COMPARATIVE-EVALUATION OF MOLECULAR TYPING OF STRAINS FROM A NATIONALEPIDEMIC DUE TO SALMONELLA BRANDENBURG BY RIBOSOMAL-RNA GENE AND IS200 PROBES AND PULSED-FIELD GEL-ELECTROPHORESIS

In Switzerland in 1992 there was a prolonged series of outbreaks of hu man salmonellosis caused by a previously rare serotype, Salmonella bra ndenburg. In order to examine the genotypic basis of the epidemic, mol ecular typing was applied to representative strains of this serovar is olated between 1983 and 1992. These included sporadic human isolates u p to 1985, isolates from unrelated geographical areas, and Swiss isola tes from humans, animals, and meat products isolated after 1991. Plasm id profiling was not found to be applicable to S. brandenburg, but chr omosomal typing was accomplished by analyzing restriction fragment len gth polymorphisms with DNA probes for three marker loci; the 16S and 2 3S rRNA genes and sites of insertion of the mobile DNA element IS200. The macrorestriction profiles of the whole genome were examined by pul sed-field gel electrophoresis, which proved to be the most discriminat ory of the typing methods. The study demonstrated the comparative valu e and complementary relationship between these typing methods for epid emiological purposes. All approaches concurred in identifying the 1992 isolates as a single genotypic clone, which was present in multiple ( food) vehicles of infection. They were distinct from sporadic isolates of this serovar and from strains of S. brandenburg isolated in other countries.