356. The discrepancy of MRSA MIC results in Etest and 4 commercially available broth micro dilution (BMD) methods: analysis of MIC measurement results of Vancomycin(VCM), Teicoplanin(TEIC), Linezolid(LZD), Daptomycin(DPT), Arbekacin(ABK) and Quinupristine/Dalfopristine (QPR/DPR) on 55 MRSA colonized isolates
Session: Poster Abstract Session: MRSA, MSSA, Enterococci
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
  • 356_IDWPOSTER.pdf (811.4 kB)
  • Background:It has been speculated that there exists discrepancy of Methicillin Resistant Staphylococcus aureus (MRSA) Minimal Inhibitory Concentration (MIC) results between variable methods. The association between higher MRSA MIC and worse clinical outcomes has been previously reported and has become a major clinical concern in managing MRSA infections. Therefore, it is clinically essential to investigate whether discrepancy exists between different MIC measurements, especially between Etest and BMD methods.

    Methods: From November 2009 to March 2011, a prospective observational study was performed at two metropolitan tertiary Emergency Departments in Japan.  Patients with high risk of MRSA colonization were determined a priori and MRSA surveillance culture was obtained. We used these previously accumulated 55 clinical MRSA isolates to compare MIC results in Etest (SYSMEX® bioMerieux Co.Ltd.) and BMD methods (BD Phoenix®, Microscan®(SIEMENS, CA, USA), Eiken® (Eiken Chemical Co., Ltd. Japan), VITEK 2 system®  (bioMérieux, Inc)). MIC results of VCM, TEIC, LZD, DPT, ABK and QPR/DPR were evaluated. The statistical analysis was performed using Wilcoxon signed rank test with continuity correction.

    Results: There was constant and significant discrepancy of MIC results in between Etest and BMD methods for MRSA  isolates.  The averages of VCM MIC were 1.86 μg/ml and 0.74 μg/ml in Etest (SYSMEX®) and in BD Phoenix®, respectively. In TEIC, they were 1.86μg/ml and 0.60μg/ml, and in LZD they were 2.55μg/ml and 1.18μg/ml. The Wilcoxon signed rank test showed p-values between Etest and BD Phoenix® were all less than 0.001 in VCM, TEIC and LZD, respectively. 

    Conclusion: Our study demonstrated the significant and constant discrepancy between Etest and BMD methods. The MIC results with Etest were significantly higher compared to those with BMD methods.

    Sari Umekawa, M.D., Yuka Kitano, M.D., Haruaki Wakatake, M.D., Shigeki Fujitani, M.D., Ph.D., Yoshihiro Masui, M.D., Ph.D. and Yasuhiko Taira, M.D., Ph.D., Emergency and Critical Care Medicine, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan


    S. Umekawa, None

    Y. Kitano, None

    H. Wakatake, None

    S. Fujitani, None

    Y. Masui, None

    Y. Taira, None

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