Limited detectability of linezolid-resistant Staphylococcus aureus by the Etest method and its improvement using enriched media

Yurika Ikeda-Dantsuji, Taiji Nakae, Koichi Ariyoshi, Hidekazu Mizuno, Hidehiko Moriyama, Osanori Nagura, Akira Suwabe, Kunihiko Fukuchi, Junichi Honda, Mitsuo Kaku, Shigeru Kohno, Hiroshige Mikamo, Yoshihito Niki, Yoshio Takesue, Kazunori Tomono, Katsunori Yanagihara, Hideaki Hanaki

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5 Citations (Scopus)

Abstract

The aim of this study was to evaluate Etest for detectability of linezolid-resistant meticillin-resistant Staphylococcus aureus (MRSA). The MIC of linezolid obtained by the Etest method in 18 linezolid-resistant strains of MRSA was compared with that obtained using standard agar and broth dilution methods according to Clinical and Laboratory Standards Institute guidelines. The mean linezolid MIC obtained by Etest in 18 linezolid-resistant strains of MRSA using Mueller- Hinton (MH) agar was 12.6-fold lower than that obtained by the agar dilution method, with the result that 78% of the linezolid-resistant strains were incorrectly classified as linezolidsusceptible. The MIC of linezolid by Etest on brain-heart infusion (BHI) agar had a mean value 2.5-fold lower than that obtained by the agar dilution method, suggesting that replacing MH agar with BHI agar considerably improved the detectability of linezolid-resistant MRSA. Use of blood agar (MH agar supplemented with 5% sheep blood) and 48 h of incubation resulted in 100% agreement with the agar and broth dilution methods. Thus, this study revealed that the Etest on MH agar and BHI agar yielded false-negative results in a significant fraction of the linezolidresistant MRSA. Hence, the use of blood agar and prolonged incubation is highly recommended for the accurate detection of linezolid-resistant MRSA using Etest.

Original languageEnglish
Pages (from-to)998-1002
Number of pages5
JournalJournal of Medical Microbiology
Volume61
Issue numberPART7
DOIs
Publication statusPublished - 2012 Jul

ASJC Scopus subject areas

  • Microbiology
  • Microbiology (medical)

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    Ikeda-Dantsuji, Y., Nakae, T., Ariyoshi, K., Mizuno, H., Moriyama, H., Nagura, O., Suwabe, A., Fukuchi, K., Honda, J., Kaku, M., Kohno, S., Mikamo, H., Niki, Y., Takesue, Y., Tomono, K., Yanagihara, K., & Hanaki, H. (2012). Limited detectability of linezolid-resistant Staphylococcus aureus by the Etest method and its improvement using enriched media. Journal of Medical Microbiology, 61(PART7), 998-1002. https://doi.org/10.1099/jmm.0.043695-0