Co-transfer of plasmids in association with conjugative transfer of mupirocin or mupirocin and penicillin resistance in methicillin-resistant Staphylococcus aureus

Two distinct strains of methicillin-resistant Staphylococcus aureus OMRSA) isolated from patients in a dermatology ward were also resistant to mupiroc in. The mupirocin resistance plasmids from both strains were indistinguisha ble by EcoRI and HindIII restriction digest analysis, except for the presen ce of genes apparently mediating penicillinase production in some transconj ugants. Conjugative transfer of the plasmid mediating mupirocin resistance from one of these strains to a recipient S. aureus was accompanied in some cases by co-transfer of plasmids mediating resistance to tetracycline or er ythromycin; in some instances a plasmid which possessed no apparent resista nce markers was also transferred. The second strain demonstrated conjugativ e transfer of penicillin and mupirocin resistance as well as transfer of a plasmid mediating gentamicin resistance, but transfer of erythromycin resis tance was not apparently plasmid-mediated.