Common R-plasmids in Staphylococcus aureus and Staphylococcus epidermidis during a nosocomial Staphylococcus aureus outbreak

During a 7-month period in 1978 to 1979, 31 patients and personnel at a Kentucky hospital were colonized or infected with a Staphylococcus aureus strain resistant to clindamycin, erythromycin, gentamicin, methicillin, penicillin, and tetracycline. S. epidermidis with similar antibiotic resistance patterns had been isolated in this hospital in the year before the S. aureus outbreak. A 32-megadalton R-plasmid, pUW3626, mediating resistance to penicillin and gentamicin, was present in these isolates and in coisolated S. epidermidis from the same outbreak. By colony hybridization, pUW3626 was homologous to gentamicin R-plasmids from staphylococci isolated in other geographic areas. Our studies suggest that the emergency of antibiotic resistance in S. Aureus may result from genetic transfer from S. epidermidis as well as from the interhospital spread of resistant staphylococci.