Molecular analysis of a hospital cafeteria-associated salmonellosis outbreak using modified repetitive element PCR fingerprinting

A hospital cafeteria-associated outbreak of gastroenteritis due to Salmonel la enterica serotype Infantis was retrospectively evaluated using modified repetitive element PCR (rep-PCR) fingerprinting with the ERIC2 and BOXA1R p rimers and computer-assisted gel analysis and dendrogram construction. Rep- PCR yielded objective between-cycler, same-strain similarity values of from 92% (composite fingerprints) to 96% (ERIC2 fingerprints). The 70 Salmonell a isolates (which included 19 serotype Infantis isolates from the hospital outbreak, 10 other serotype Infantis isolates, and 41 isolates representing 14 other serotypes) were resolved well to the serotype level with each of the three fingerprint types (ERIC2, BOXA1R, and composite). Rep-PCR typing uncovered several historical serotyping errors and provided presumptive ser otype assignments for other isolates with incomplete or undetermined seroty pes. Analysis of replicate fingerprints for each isolate, as generated on t wo different thermal cyclers, indicated that most of the seeming subserotyp e discrimination noted in single-cycler dendrograms actually represented as say variability, since it was not reproducible in combined-cycler dendrogra ms. Rep-PCR typing, which would have been able to identify the presence of the hospital-associated serotype Infantis outbreak after the second outbrea k isolate, could be used as a simple surrogate for serotyping by clinical m icrobiology laboratories that are equipped for diagnostic PCR.