Genetic Analysis of a High-Level Vancomycin-Resistant Isolate of Staphylococcus aureus

Vancomycin is usually reserved for treatment of serious infections, including those caused by multidrug-resistant Staphylococcus aureus . A clinical isolate of S. aureus with high-level resistance to vancomycin (minimal inhibitory concentration = 1024 μg/ml) was isolated in June 2002. This isolate harbored a 57.9-kilobase multiresistance conjugative plasmid within which Tn 1546 ( vanA ) was integrated. Additional elements on the plasmid encoded resistance to trimethoprim ( dfrA ), β-lactams ( blaZ ), aminoglycosides ( aacA-aphD ), and disinfectants ( qacC ). Genetic analyses suggest that the long-anticipated transfer of vancomycin resistance to a methicillin-resistant S. aureus occurred in vivo by interspecies transfer of Tn 1546 from a co-isolate of Enterococcus faecalis .