Ann Lab Med 2018; 38(2): 155-159
Prevalence of blaZ Gene and Performance of Phenotypic Tests to Detect Penicillinase in Staphylococcus aureus Isolates from Japan
Yoshiko Takayama, M.T.1,2,*, Takashi Tanaka, M.T.2,3,*, Koko Oikawa, M.T.1, Naoki Fukano, M.T.1, Mieko Goto, M.T.2, and Takashi Takahashi, M.D.2
Division of Clinical Laboratory1, Byotai-Seiri Laboratory, Tokyo; Laboratory of Infectious Diseases2, Kitasato Institute for Life Sciences, Kitasato University, Tokyo; Division of Clinical Laboratory Examination3, Teikyo Junior College, Tokyo, Japan
Corresponding author: Takashi Takahashi
Laboratory of Infectious Diseases, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
Tel: +81-3-5791-6428
Fax: +81-3-5791-6441
*These authors equally contributed to this study.
Received: April 10, 2017; Revised: May 10, 2017; Accepted: October 13, 2017; Published online: March 1, 2018.
© Korean Society for Laboratory Medicine. All rights reserved.

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Guidelines recommend that clinical laboratories perform phenotypic tests (nitrocefin-based test and penicillin 10-U [P10] or 1-U [P1] zone edge tests) to detect penicillinase in Staphylococcus aureus isolates. This study aimed to assess the prevalence of blaZ encoding penicillinase and perform various phenotypic tests in S. aureus isolates from Japan. We prospectively collected 200 methicillin-susceptible S. aureus isolates from June 2015 to January 2016 and performed six phenotypic tests (nitrocefin-based test, P10 zone edge test/P10 diffusion test, penicillin 2-U [P2] zone edge test/P2 diffusion test, and cloverleaf test) on each sample. We confirmed the presence of blaZ (two blaZ-positive isolates) using PCR. Using blaZ PCR as a standard, we observed a low sensitivity (50%) and positive predictive value (PPV, 50%) of the nitrocefin-based test, low PPV (18.2%) of the P10 zone edge test, low sensitivity (50%) of the P10 diffusion test, low PPV (50% and 22.2%) of the P2 zone edge test and P2 diffusion test, respectively, and low sensitivity (50%) of the cloverleaf test. These data suggest a low performance (sensitivity and PPV) of these six phenotypic tests because of the low prevalence (1%) of blaZ in S. aureus isolates from Japan.
Keywords: blaZ, Phenotypic tests, Penicillinase, Staphylococcus aureus, Japan

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