Objectives

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is becoming the method of choice for bacterial identification. However, correct identification by MALDI-TOF of closely related microorganisms such as viridans streptococci is still cumbersome, especially in the identification of S. pneumoniae. By making use of additional spectra peaks for S. pneumoniae and other viridans group streptococci (VGS). We re-identified viridans streptococci that had been identified and characterized by molecular and phenotypic techniques by MALDI-TOF.

Methods

VGS isolates (n = 579), 496 S. pneumoniae and 83 non-S. pneumoniae were analysed using MALDI-TOF MS and the sensitivity and specificity of MALDI-TOF MS was assessed. Hereafter, mass spectra analysis was performed. Presumptive identification of proteins represented by discriminatory peaks was performed by molecular weight matching and the corresponding nucleotides sequences against different protein databases.

Results

Using the Bruker reference library, 495 of 496 S. pneumoniae isolates were identified as S. pneumoniae and one isolate was identified as non-S. pneumoniae. Of the 83 non-S. pneumoniae isolates, 37 were correctly identified as non-S. pneumoniae, and 46 isolates as S. pneumoniae. The sensitivity of the MALDI-TOF MS was 99.8% (95% confidence interval (CI) 98.9–100) and the specificity was 44.6% (95% CI 33.7–55.9). Eight spectra peaks were mostly present in one category (S. pneumoniae or other VGS) and absent in the other category and inversely. Two spectra peaks of these (m/z 3420 and 3436) were selected by logistic regression to generate three identification profiles. These profiles could differentiate between S. pneumoniae and other VGS with high sensitivity and specificity (99.4% and 98.8%, respectively).

Conclusions

Spectral peaks analysis based identification is a powerful tool to differentiate S. pneumoniae from other VGS species with high specificity and sensitivity and is a useful method for pneumococcal identification in carriage studies. More research is needed to further confirm our findings. Extrapolation of these results to clinical strains need to be deeply investigated.

中文翻译：

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通过基质辅助激光解吸/电离飞行时间质谱法区分肺炎链球菌和其他绿脓杆菌链球菌。

目标

基质辅助激光解吸/电离飞行时间质谱仪（ MALDI-TOF MS）成为细菌鉴定的首选方法。然而，特别是在肺炎链球菌的鉴定中，通过MALDI-TOF正确鉴定紧密相关的微生物例如绿藻链球菌仍然是麻烦的。通过利用肺炎链球菌和其他绿藻类链球菌（VGS）的其他光谱峰。我们重新鉴定了通过分子和表型技术已通过MALDI-TOF鉴定和鉴定的绿色蛇毒链球菌。

方法

使用MALDI-TOF MS分析了VGS分离株（n  = 579），496例肺炎链球菌和83例非肺炎链球菌，并评估了MALDI-TOF MS的敏感性和特异性。此后，进行质谱分析。通过分子量匹配和针对不同蛋白质数据库的相应核苷酸序列来进行鉴定性蛋白质鉴定。

结果

使用布鲁克参考文库，将496个肺炎链球菌分离物中的495个鉴定为肺炎链球菌，并将一个分离物鉴定为非肺炎链球菌。在83株非肺炎链球菌中，正确鉴定出37株为非S肺炎链球菌。肺炎链球菌和46株肺炎链球菌。MALDI-TOF MS的灵敏度为99.8％（95％置信区间（CI）98.9–100），特异性为44.6％（95％CI 33.7–55.9）。一类中主要存在八个光谱峰（肺炎链球菌或其他VGS），而在其他类别中则相反。通过逻辑回归选择这些峰的两个光谱峰（m / z 3420和3436）以生成三个识别曲线。这些图谱可以高灵敏度和高特异性（分别为99.4％和98.8％）区分肺炎链球菌和其他VGS。

结论

基于谱峰分析的鉴定是区分肺炎链球菌与其他VGS种类的强大工具，具有很高的特异性和敏感性，并且是在运输研究中鉴定肺炎球菌的有用方法。需要更多的研究来进一步证实我们的发现。将这些结果外推至临床菌株需要深入研究。