Molecular study on Salmonella enteritidis strains from a nosocomial gastroenteritis outbreak

A molecular epidemiological analysis was carried out on S. enteritidis isolates identified at the Central Italy Enterobacteriaceae Center during 1986. 26 of these were from a diarrhoeal disease outbreak, which occurred in the period April-June at the "S. Chiara" Hospital, Pisa. All S. enteritidis strains harboured a virulence-encoding 39 MDa plasmid. The nosocomial isolates made in June 1986 carried an additional non-conjugative plasmid of 75 MDa, associated with the streptomycin-resistance. In contrast, the nosocomial S. enteritidis strains isolated during the period April-May and 16 isolates from the same geographic area were susceptible to antibiotics and showed a different plasmid pattern. According to the plasmid profile and antibiotic resistance pattern analysis, it could be argued that the hospital cases of S. enteritidis infection occurring after May 1986 are attributable to a strain having different origin from the strain circulating in April-May 1986.