Nosocomial Infections with Gentamicin-Resistant Staphylococcus aureus: Plasmid Analysis as an Epidemiologic Tool

Abstract

Infection with strains of Staphylococcus aureus resistant to gentamicin (SARG) was identified in 22 infants in the high-risk nursery of a municipal hospital during the period October 1, 1976–August 31, 1977; no infections with SARG had previously been encountered. Infection with SARG also occurred in 20 adults on the medical and surgical services and in 12 patients in the burn unit. Patients infected with SARG more frequently had been treated with gentamicin and had been hospitalized longer prior to infection than patients infected with strains of S. aureus susceptible to gentamicin. However, sites of infection, hospital service involved, and the death rates during hospitalization were similar for the two groups. Isolates of two different phage types had the same pattern of antibiotic resistance. Five representative isolates (two phage types) were analyzed for plasmid content, and their plasmids were analyzed by restriction endonuclease digestion. Two isolates contained identical plasmids, and EcoRI restriction endonuclease fragments appeared to be common between plasmids of isolates from patients on different services at different times. Thus, spread of resistance probably involved both dissemination of a single plasmid among different isolates and spread of multiple plasmids containing the same type of resistance determinants.