Division of Clinical Laboratory, Byotai-Seiri Laboratory, Tokyo, Japan.
Laboratory of Infectious Diseases, Kitasato Institute for Life Sciences, Kitasato University, Tokyo, Japan.
Ann Lab Med. 2018 Mar;38(2):155-159. doi: 10.3343/alm.2018.38.2.155.
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.
指南建议临床实验室对金黄色葡萄球菌分离株进行表型检测（硝基头孢菌素试验和青霉素 10-U [P10]或 1-U [P1] 抑菌圈边缘试验），以检测青霉素酶。本研究旨在评估日本金黄色葡萄球菌分离株中 blaZ 编码青霉素酶的流行率，并进行各种表型检测。我们前瞻性地收集了 200 株耐甲氧西林金黄色葡萄球菌分离株，从 2015 年 6 月至 2016 年 1 月，对每个样本进行了 6 种表型检测（硝基头孢菌素试验、P10 抑菌圈边缘试验/P10 扩散试验、青霉素 2-U [P2] 抑菌圈边缘试验/P2 扩散试验和三叶试验）。我们使用 PCR 确认 blaZ 的存在（两株 blaZ 阳性分离株）。使用 blaZ PCR 作为标准，我们观察到硝基头孢菌素试验的敏感性（50%）和阳性预测值（PPV，50%）较低，P10 抑菌圈边缘试验的 PPV 较低（18.2%），P10 扩散试验的敏感性较低（50%），P2 抑菌圈边缘试验和 P2 扩散试验的 PPV 分别较低（50%和 22.2%），三叶试验的敏感性较低（50%）。这些数据表明，由于日本金黄色葡萄球菌分离株中 blaZ 的低流行率（1%），这 6 种表型检测的性能（敏感性和 PPV）较低。
