AAC Accepts, published online ahead of print on 30 October 2006

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Antimicrob. Agents Chemother. doi:10.1128/AAC.00576-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

High-Level Vancomycin-Resistant Staphylococcus aureus (VRSA)

Linda M. Weigel, Rodney M. Donlan^*, Dong Hyeon Shin, Bette Jensen, Nancye C. Clark, Linda McDougal, Wenming Zhu, Kimberlee A. Musser, Jill Thompson, Donna Kohlerschmidt, Nellie Dumas, Ronald J. Limberger, and Jean B. Patel

Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia; Wadsworth Center, New York State Department of Health, Albany, New York

^* To whom correspondence should be addressed. Email: lweigel{at}cdc.gov,

Glycopeptides such as vancomycin are the treatment of choice for infections due to methicillin-resistant Staphylococcus aureus. This study describes the identification of high-level vancomycin-resistant S. aureus (VRSA) isolates in a polymicrobial biofilm within an indwelling nephrostomy tube in a patient in New York. S. aureus, Enterococcus faecalis, E. faecium, Micrococcus species, Morganella morganii, and Pseudomonas aeruginosa were isolated from the biofilm. For VRSA isolates, vancomycin MICs ranged from 32 to >128 µg/ml. VRSA were also resistant to aminoglycosides, fluoroquinolones, macrolides, penicillin, and tetracycline, but remained susceptible to chloramphenicol, linezolid, rifampin, and trimethoprim-sulfamethoxazole. The vanA gene was localized to a plasmid of 100 kb in VRSA and E. faecium isolates from the biofilm. Plasmid analysis revealed that the VRSA acquired the 100-kb E. faecium plasmid, which was then maintained without integration into the MRSA plasmid. The tetracycline resistance genes, tet(U) and tet(S), not previously detected in S. aureus isolates, were identified in the VRSA isolates. Additional resistance elements in the VRSA included a multiresistance gene cluster, ermB-aadE-sat4-aphA-3, msrA (macrolide efflux), and the bifunctional aminoglycoside resistance gene, aac(6')-aph(2")-Ia. Multiple combinations of resistance genes among the various isolates of staphylococci and enterococci, including vanA, tet(S), and tet(U), illustrate the dynamic nature of gene acquisition and loss within and between bacterial species throughout the course of infection. The potential for interspecies transfer of antimicrobial resistance genes, including resistance to vancomycin, may be enhanced by the microenvironment of a biofilm.

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