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Journal of Clinical Microbiology, June 2004, p. 2398-2402, Vol. 42, No. 6
0095-1137/04/$08.00+0     DOI: 10.1128/JCM.42.6.2398-2402.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Relationship of MIC and Bactericidal Activity to Efficacy of Vancomycin for Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia

George Sakoulas,1* Pamela A. Moise-Broder,2 Jerome Schentag,2 Alan Forrest,2 Robert C. Moellering Jr.,3 and George M. Eliopoulos3

Crystal Run Healthcare, Middletown,1 School of Pharmacy, State University of New York at Buffalo, Buffalo, and CPL Associates LLC, Amherst, New York,2 Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts3

Received 26 November 2003/ Returned for modification 18 January 2004/ Accepted 25 February 2004

We attempted to find a relationship between the microbiological properties of bloodstream isolates of methicillin-resistant Staphylococcus aureus (MRSA) and the efficacy of vancomycin in the treatment of bacteremia. Vancomycin susceptibility testing was performed, and bactericidal activity was determined for 30 isolates from 30 different patients with MRSA bacteremia for whom clinical and microbiological outcome data were available. The majority of these patients had been previously enrolled in multicenter prospective studies of MRSA bacteremia refractory to conventional vancomycin therapy. Logistic regression found a statistically significant relationship between treatment success with vancomycin and decreases in both vancomycin MICs (<=0.5 µg/ml versus 1.0 to 2.0 µg/ml; P = 0.02) and degree of killing (reduction in 1og10 CFU/milliliter) by vancomycin over 72 h of incubation in vitro (P = 0.03). For MRSA isolates with vancomycin MICs <= 0.5 µg/ml, vancomycin was 55.6% successful in the treatment of bacteremia whereas vancomycin was only 9.5% effective in cases in which vancomycin MICs for MRSA were 1 to 2 µg/ml. Patients with MRSA that was more effectively killed at 72 h by vancomycin in vitro had a higher clinical success rate with vancomycin therapy in the treatment of bacteremia (log10 < 4.71 [n = 9], 0%; log10 4.71 to 6.26 [n = 13], 23.1%; log10 > 6.27 [n = 8], 50%). We conclude that a significant risk for vancomycin treatment failure in MRSA bacteremia begins to emerge with increasing vancomycin MICs well within the susceptible range. Elucidating the mechanisms involved in intermediate-level glycopeptide resistance in S. aureus should begin by examining bacteria that begin to show changes in vancomycin susceptibility before the development of obvious resistance. Prognostic information for vancomycin treatment outcome in MRSA bacteremia may also be obtained by testing the in vitro bactericidal potency of vancomycin.

* Corresponding author. Mailing address: Crystal Run Healthcare, 155 Crystal Run Rd., Middletown, NY 10941. Phone: (845) 703-6100, ext. 4233. Fax: (845) 361-1156. E-mail: gsakoulas{at}crystalrunhealthcare.com.

Journal of Clinical Microbiology, June 2004, p. 2398-2402, Vol. 42, No. 6
0095-1137/04/$08.00+0     DOI: 10.1128/JCM.42.6.2398-2402.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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Copyright © 2004 by the American Society for Microbiology. All rights reserved.