Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland.
J Clin Microbiol. 2013 Jun;51(6):1834-40. doi: 10.1128/JCM.02654-12. Epub 2013 Apr 3.
This study compared three sample preparation methods (direct transfer, the direct transfer-formic acid method with on-target formic acid treatment, and ethanol-formic acid extraction) for the identification of Gram-positive cocci with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). A total of 156 Gram-positive cocci representing the clinically most important genera, Aerococcus, Enterococcus, Staphylococcus, and Streptococcus, as well as more rare genera, such as Gemella and Granulicatella, were analyzed using a Bruker MALDI Biotyper. The rate of correct genus-level identifications was approximately 99% for all three sample preparation methods. The species identification rate was significantly higher for the direct transfer-formic acid method and ethanol-formic acid extraction (both 77.6%) than for direct transfer (64.1%). Using direct transfer-formic acid compared to direct transfer, the total time to result was increased by 22.6%, 16.4%, and 8.5% analyzing 12, 48, and 96 samples per run, respectively. In a subsequent prospective study, 1,619 clinical isolates of Gram-positive cocci were analyzed under routine conditions by MALDI-TOF MS, using the direct transfer-formic acid preparation, and by conventional biochemical methods. For 95.6% of the isolates, a congruence between conventional and MALDI-TOF MS identification was observed. Two major limitations were found using MALDI-TOF MS: the differentiation of members of the Streptococcus mitis group and the identification of Streptococcus dysgalactiae. The Bruker MALDI Biotyper system using the direct transfer-formic acid sample preparation method was shown to be a highly reliable tool for the identification of Gram-positive cocci. We here suggest a practical algorithm for the clinical laboratory combining MALDI-TOF MS with phenotypic and molecular methods.
本研究比较了三种样品制备方法（直接转移、带目标甲酸处理的直接转移-甲酸法和乙醇-甲酸提取法），用于使用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）鉴定革兰氏阳性球菌。使用 Bruker MALDI Biotyper 分析了代表临床最重要属的 156 株革兰氏阳性球菌，包括 Aerococcus、Enterococcus、Staphylococcus 和 Streptococcus，以及更罕见的属，如 Gemella 和 Granulicatella。三种样品制备方法的正确属水平鉴定率均约为 99%。直接转移-甲酸法和乙醇-甲酸提取法的种鉴定率明显高于直接转移法（分别为 77.6%和 64.1%）。与直接转移相比，使用直接转移-甲酸法分别分析 12、48 和 96 个样本/运行时，结果总时间分别增加了 22.6%、16.4%和 8.5%。在随后的前瞻性研究中，使用 MALDI-TOF MS 通过直接转移-甲酸制备方法，在常规条件下分析了 1619 株临床分离的革兰氏阳性球菌，同时还使用了常规生化方法。对于 95.6%的分离株，观察到常规和 MALDI-TOF MS 鉴定之间的一致性。使用 MALDI-TOF MS 发现了两个主要限制：链球菌米蒂斯组成员的区分和停乳链球菌的鉴定。使用直接转移-甲酸样品制备方法的 Bruker MALDI Biotyper 系统被证明是一种高度可靠的革兰氏阳性球菌鉴定工具。我们在此建议一种将 MALDI-TOF MS 与表型和分子方法相结合的临床实验室实用算法。
