Plasmid profile analysis of salmonellae in a large-animal hospital

The plasmid profiles of salmonellae isolated from the patients and environment of the Purdue Large Animal Hospital were used us markers to identify strains and to assess impact of improvements in hospital operation on nosocomial salmonellosis. Plasmid profile analysis proved to be more sensitive than either serotyping or antimicrobil susceptibility testing in identifying Salmonella isolates. During June and July 1983, 29 of 34 salmonellae isolated were one of three strains with distinct plasmid profiles: one S. typhimurium var. Copenhagen, and two S. muenchen. Each of these strains was isolated from at least one patient and two environmental sites, suggesting the possibility that infections were hospital-acquired. Patient and environmental sampling was repeated in June and July 1984, after improvements had been made in hospital traffic flow and sanitaton. In contrast to 1983, only seven isolates, representing six strains not seen previously, were obtained in 1984. None of these strains was isolated from both patient and environmental sources. The results indicate that the high incidence of clinical salmonellosis in 1983 was largely due to nosocomial infections. The decrease in the incidence of salmonellosis and the absence of the 1983 strains from samples taken in 1984 were presumed to be to improvements made in hospital operation. This study demonstrates the value of plasmid analysis in monitoring nosocomial salmonellosis in a veterinary hospital.