Daptomycin bactericidal activity and correlation between disk and broth microdilution method results in testing of Staphylococcus aureus strains with decreased susceptibility to vancomycin

Daptomycin bactericidal activity and correlation between disk and broth microdilution method results in testing of Staphylococcus aureus strains with decreased susceptibility to vancomycin

Author Autor UNIFESP Google Scholar
Fritsche, T. R. Google Scholar
Jones, R. N. Google Scholar
Institution JMI Labs
Universidade Federal de São Paulo (UNIFESP)
Tufts Univ
Abstract A total of 207 Staphylococcus aureus strains, including 105 well-characterized strains with decreased susceptibility to vancomycin (17 vancomycin-intermediate S. aureus [VISA] and 88 heteroresistant VISA [hVISA] strains) and 102 wild-type methicillin-resistant S. aureus (MRSA-WT) strains were tested by reference/standardized broth microdilution and disk diffusion methods, as well as by Etest (AB BIODISK, Solna, Sweden), against daptomycin and vancomycin. the lowest concentration of antimicrobial agent that killed >= 99.9% of the initial inoculum was defined as the minimum bactericidal concentration (MBC) endpoint, and time-kill curves were performed in selected strains to further evaluate bactericidal activity. All MRSA-WT and hVISA strains were inhibited by <= 1 g/ml of daptomycin, while the VISA strains showed slightly higher daptomycin MICs (range, 0.5 to 4 mu g/ml). All daptomycin MBC results were at the MIC or twofold higher. in contrast, 14.7% of MRSA-WT, 69.3% of hVISA, and all VISA strains showed a vancomycin MBC/MIC ratio of :32 or an MBC of 16 mu g/ml (tolerant). the correlation coefficients between broth microdilution and disk diffusion method results were low for daptomycin (0.07) and vancomycin (0.11). Eight (3.8%) strains (all hVISA or VISA) were nonsusceptible to daptomycin by broth microdilution methods but susceptible by the disk diffusion method. for vancomycin, 35 (16.9%) strains were nonsusceptible by broth microdilution methods but susceptible by disk diffusion methods. in conclusion, daptomycin was highly bactericidal against S. aureus strains, and its bactericidal activity was not affected by decreased susceptibility to vancomycin. in contrast, many (one in seven) contemporary MRSA-WT, the majority of hVISA, and all VISA strains showed vancomycin MBC/MIC ratios consistent with tolerance, a predictor of poor clinical response. Disk diffusion tests generally failed to detect strains categorized as nonsusceptible to daptomycin or vancomycin by the reference broth microdilution method or Etest, and reassessment of breakpoints should be immediately attempted for MIC methods suggested as the test of choice.
Language English
Date 2006-07-01
Published in Antimicrobial Agents and Chemotherapy. Washington: Amer Soc Microbiology, v. 50, n. 7, p. 2330-2336, 2006.
ISSN 0066-4804 (Sherpa/Romeo, impact factor)
Publisher Amer Soc Microbiology
Extent 2330-2336
Origin http://dx.doi.org/10.1128/AAC.01491-05
Access rights Open access Open Access
Type Article
Web of Science ID WOS:000238721200008
URI http://repositorio.unifesp.br/handle/11600/28993

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