Identification of mycobacteria by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) requires not only a good protein extraction protocol but also an adequate cutoff score in order to provide reliable results. The aim of this study was to assess the cutoff scores proposed by the MALDI-TOF MS system for mycobacterial identification. A total of 693 clinical isolates from a liquid medium and 760 from a solid medium were analyzed, encompassing 67 different species of nontuberculous mycobacteria (NTM). MALDI-TOF MS identified 558 (80.5%) isolates from the liquid medium and 712 (93.7%) isolates from the solid medium with scores of ≥1.60. Among these, four (0.7%) misidentifications were obtained from the liquid medium and four (0.5%) from the solid medium. With regard to species diversity, MALDI-TOF MS successfully identified 64 (95.5%) different species, while PCR-reverse hybridization (GenoType Mycobacterium CM and AS assays) identified 24 (35.8%) different species. With MALDI-TOF MS scores of ≥2, all isolates were correctly identified, and with scores in the range from 1.60 to 1.99, most isolates were correctly identified, except for Mycobacterium angelicum, M. parascrofulaceum, M. peregrinum, M. porcinum, and M. gastri. In conclusion, MALDI-TOF MS is a useful method for identifying a large diversity of NTM species. A score threshold of 1.60 proved useful for identifying almost all the isolates tested; only a few species required a higher score (≥2.00) to obtain a valid definitive identification.

中文翻译：

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准确评估非结核分枝杆菌的MALDI Biotyper解释标准的评估。

通过基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）鉴定分枝杆菌不仅需要良好的蛋白质提取方案，而且还需要足够的分界值才能提供可靠的结果。这项研究的目的是评估由MALDI-TOF MS系统提出的用于分枝杆菌鉴定的临界值。共分析了来自液体培养基的693种临床分离株和来自固体培养基的760种临床分离株，包括67种不同的非结核分枝杆菌（NTM）。MALDI-TOF MS从液体培养基中鉴定出558个（80.5％）分离物，从固体培养基中鉴定出712个（93.7％）分离物，得分≥1.60。其中，从液体介质中获得了四个（0.7％）错误标识，从固体介质中获得了四个（0.5％）错误标识。关于物种多样性，分枝杆菌CM和AS测定）鉴定出24个（35.8％）不同的物种。随着≥2MALDI-TOF MS的分数，所有分离株正确识别，并与得分的范围为1.60〜1.99，最分离物正确识别，除了结核分枝angelicum，M. parascrofulaceum，M. peregrinum，M. porcinum，和M. gastri。总之，MALDI-TOF MS是鉴定NTM物种多样性的有用方法。事实证明，分数阈值为1.60可用于鉴定几乎所有测试的分离株。只有少数物种需要更高的分数（≥2.00）才能获得有效的确定性标识。