CONVENTIONAL AND MOLECULAR APPROACHES TO ISOLATES OF SALMONELLA HADARFROM SPORADIC AND EPIDEMIC CASES

In September 1994 an outbreak of gastroenteritis occurred in 437 peopl e who had consumed lunch in the canteen of a factory in Central Italy. Salmonella sp. was isolated from stools of 99 patients and in 73 of t hem Salmonella hadar was identified. This is the first outbreak caused by this serotype described in Italy. In order to examine the genotypi c basis of the epidemic strains, molecular typing was applied to spora dic strains isolated before and after the outbreak episode. For this p urpose phage type, resistance to antibiotics, DNA plasmid profile and sites of insertion of the mobile element of IS200 were determined. The epidemic strains were genetically distinct from the non-epidemic isol ates; they were shown to be phage type 26, harbouring four small plasm ids, were resistant to nalidixic acid and showed a unique characterist ic IS200 fingerprint. The typing methods used in this study allowed th e identification and discrimination of the outbreak strains from relat ed isolates. They can thus be considered as a tool for epidemiological purposes. In addition we should point out the emerging resistance to nalidixic acid, largely used in veterinary medicine, in Salm. hadar.