POLYMORPHISM OF RIBOSOMAL-RNA GENES AND PLASMID ANALYSIS IN THE TYPING OF SALMONELLA-ENTERICA SEROVAR ENTERITIDIS FROM A SPANISH HEALTH AREA

A molecular epidemiological study of Salmonella enterica serovar Enter itidis (S. enteritidis) in a Spanish Health Area was carried out using two genotypic methods: polymorphism of rRNA genes (ribotyping) and pl asmid analysis. The series included 100 isolates randomly selected fro m among those collected over the period 1984-92 (50 from sporadic epis odes and 50 from 10 outbreaks). Ribotyping using HindIII, SmaI, and Ec oRI showed a notable degree of homogeneity within Enteritidis serovar, it being able to discriminate only 1, 2, and 3 ribotypes, respectivel y. Such data suggest that there are a limited number of types or clona l lines, of which only one was widely disseminated within the health a rea under study (including 90% of isolates from sporadic episodes and all of those from outbreaks). Twelve plasmid profiles were differentia ted. Sixty isolates carried only the virulence plasmid of 36 Md; where as 24 isolates, grouped into 10 profiles, carried the 36 Md together w ith other plasmids; 7 isolates carried only other plasmids and 9 isola tes were plasmid free. The combination of results from both methods re vealed 15 subtypes, 9 of these including two or more isolates, one sub type being endemic and predominant (54% of the sporadic isolates and i solates from 6 outbreaks).