Evaluation of VITEK 2 Compact and VITEK MS in the identification of coagulase-negative staphylococci isolated from blood cultures

ABSTRACT Introduction: In most clinical laboratories, coagulase-negative staphylococci (CNS) are classified through their biochemical characteristics using traditional and/or automated phenotypic methods. However, identification by phenotypic method is a great challenge despite the improvement in identification by automated systems in recent years. Objective: The main objective was to compare the identification of CNS between two automated methods: phenotypic (VITEK® 2 Compact, bioMérieux) and mass spectrometry (MALDI-TOF VITEK® MS, bioMérieux). Materials and method: 133 CNS isolates from whole blood samples from September 2015 to May 2016 were analyzed. Results: All the 133 isolates were identified by VITEK® 2 Compact as CNS, whereas VITEK MS did not identify seven, and there was uncertainty among three species in one isolate. The two devices had a concordance of 92.8% (117/126) of which: 56 Staphylococcus epidermidis, 34 Staphylococcus hominis ssp. hominis, 15 Staphylococcus haemolyticus, 10 Staphylococcus capitis, one Staphylococcus cohnii ssp. urealyticus and one Staphylococcus sciuri. There was disagreement in identification of S. lugdunensis and S. aureus. Conclusion: Through the analysis between the two devices and based on scientific articles comparing the methods involved in the study, it was possible to observe the great biochemical similarity among the coagulase-negative staphylococci species, this being the main limitation of the phenotypic method. The VITEK MS equipment showed high discrimination between species when compared to the gold standard method, besides being rapid and easy to use.

摘要
引言：在多数临床实验室中，凝固酶阴性葡萄球菌（coagulase-negative staphylococci, CNS）通常依托传统及/或自动化表型方法，基于其生化特征完成分类。尽管近年来自动化鉴定系统的性能有所提升，但表型方法的菌种鉴定仍存在极大挑战。
研究目的：本研究旨在对比两种自动化鉴定方法对凝固酶阴性葡萄球菌的鉴定效果：表型鉴定法（VITEK® 2 Compact，生物梅里埃（bioMérieux））与质谱鉴定法（MALDI-TOF VITEK® MS，生物梅里埃（bioMérieux））。
材料与方法：本研究分析了2015年9月至2016年5月期间，全血样本中分离得到的133株凝固酶阴性葡萄球菌菌株。
结果：全部133株菌株均经VITEK® 2 Compact鉴定为凝固酶阴性葡萄球菌，而VITEK MS未能完成7株菌株的鉴定，另有1株菌株的3个菌种鉴定结果存在不确定性。两种检测方法的鉴定一致性达92.8%（117/126），其中涵盖：56株表皮葡萄球菌（Staphylococcus epidermidis）、34株人葡萄球菌人亚种（Staphylococcus hominis ssp. hominis）、15株溶血葡萄球菌（Staphylococcus haemolyticus）、10株头葡萄球菌（Staphylococcus capitis）、1株解脲科恩葡萄球菌（Staphylococcus cohnii ssp. urealyticus）以及1株松鼠葡萄球菌（Staphylococcus sciuri）。两种方法在路邓葡萄球菌（S. lugdunensis）与金黄色葡萄球菌（S. aureus）的鉴定结果上存在分歧。
结论：通过对两种检测方法的分析，并结合本研究涉及方法的相关科学文献，可观察到凝固酶阴性葡萄球菌各菌种间具有高度相似的生化特征，这也是表型鉴定方法的核心局限性。相较于金标准方法，VITEK MS设备对菌种的分辨能力优异，且具备检测快速、操作简便的优势。