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The first clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA) that exhibited high-level resistance to vancomycin was described last year in a patient who was also colonized with vancomycin-resistant enterococcus (VRE) (see Journal Watch Infectious Diseases Apr 25 2003). New genetic analysis confirms that vancomycin-resistant S. aureus (VRSA) arose by acquisition of a gene from VRE.
PCR confirmed that the VRSA isolate contained the vanA gene that confers high-level resistance to vancomycin in VRE. The vanA localized to a plasmid in the VRSA isolate and appeared to have been added to a plasmid present in an MRSA isolate from the same patient. The vanA-containing plasmid from the patient's VRE isolate and the VRSA plasmid wer…