Polymorphism of rRNA 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 Enteritidis (S. enteritidis) in a Spanish Health Area was carried out using two genotypic methods; polymorphism of rRNA genes (ribotyping) and plasmid analysis. The series included 100 isolates randomly selected from among those collected over the period 1984-92 (50 from sporadic episodes and 50 from 10 outbreaks). Ribotyping using HindIII, SmaI, and EcoRI showed a notable degree of homogeneity within Enteritidis serovar, it being able to discriminate only 1, 2, and 3 ribotypes, respectively. Such data suggest that there are a limited number of types or clonal lines, of which only one was widely disseminated within the health area under study (including 90% of isolates from sporadic episodes and all of those from outbreaks). Twelve plasmid profiles were differentiated. Sixty isolates carried only the virulence plasmid of 36 Md; whereas 24 isolates, grouped into 10 profiles, carried the 36 Md together with other plasmids; 7 isolates carried only other plasmids and 9 isolates were plasmid free. The combination of results from both methods revealed 15 subtypes, 9 of these including two or more isolates, one subtype being endemic and predominant (54% of the sporadic isolates and isolates from 6 outbreaks).