Gentamicin resistance in methicillin-resistant Staphylococcus aureus.

Gentamicin resistance has been studied in methicillin-resistant Staphylococcus aureus (MRSA) strains, from Royal Melbourne Hospital (RMH) and Sydney. Gentamicin resistance was transferred in mixed cultures to a plasmid free strain, and the determinants were examined. The Sydney strain had high level resistance to gentamicin, tobramycin, kanamycin and neomycin which was carried on a c.34 megadalton plasmid. The gentamicin resistant RMH isolates all had a determinant which conferred low level resistance to gentamicin, tobramycin and kanamycin and appeared to be chromosomal in one isolate, on a plasmid of c.28.5 megadaltons in another and on a plasmid of c.18 megadaltons in the other isolates. It is suggested that a gentamicin resistance transposon is being transferred in the MRSA at RMH.