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Journal of Clinical Microbiology, May 2005, p. 2494-2496, Vol. 43, No. 5
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.5.2494-2496.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Unstable Vancomycin Heteroresistance Is Common among Clinical Isolates of Methiciliin-Resistant Staphylococcus aureus
Nottasorn Plipat,1*
Gilat Livni,2
Heidi Bertram,3 and
Richard B. Thomson Jr.3
Division of Infectious Diseases, Department of Pediatrics, Siriraj Hospital, Mahidol University, Bangkok, Thailand,1
Schneider Children's Medical Center of Israel, Tel Aviv, Israel,2
Department of Pathology and Laboratory Medicine, Evanston Northwestern Healthcare, Evanston, Illinois, and Northwestern University Feinberg School of Medicine, Chicago, Illinois3
Received 4 September 2004/
Returned for modification 17 October 2004/
Accepted 24 December 2004
We tested 109 unique, vancomycin-susceptible, methicillin-resistant Staphylococcus aureus (MRSA) strains for vancomycin heteroresistance by a selection method, i.e., step-wise exposure of large inoculums to increasing concentrations of vancomycin. Although no strains demonstrated stable heteroresistance, 81 strains (74%) demonstrated unstable heteroresistance. Unstable heteroresistance is common among clinical isolates of MRSA and may represent a cause of therapeutic failure.
* Corresponding author. Mailing address: Division of Pediatric Infectious Diseases, Department of Pediatrics, Siriraj Hospital, Mahidol University, 2 Prannok Road, Bangkoknoi, Bangkok 10700, Thailand. Phone: 66-2-4180545. Fax: 66-2-4180544 E-mail:
nplipat{at}msn.com.
Journal of Clinical Microbiology, May 2005, p. 2494-2496, Vol. 43, No. 5
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.5.2494-2496.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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