Background

Recently, MALDI-TOF has emerged as a quick tool for bacterial typing. The aim was to evaluate if MALDI-TOF based typing of Legionella pneumophila can achieve the same discriminatory power as that of the Sequence Based Typing (SBT) method.

Methods

The Sequence Type (ST) was obtained from the 90 strains included in the training set and an in-house MALDI-TOF library based on the Main Spectra Profile (MSP) was generated for the identification of such ST. Then, our library was validated by three procedures: a) creating a dendrogram, b) searching for specific peaks present exclusively in each MSP entry, and c) analysing a validation set composed of 14 strains with known ST. Fully characterized L. pneumophila ATCC 33152, which belongs to ST 36, was used as a control strain. Results: In the training set, 17 strains belonged to ST 1, 1 to ST 20, 63 to ST 22, 1 to ST 146, 6 to ST 578, and 2 to ST 1086. Specific peaks present in each MSPs spectrum, which are considered type-specific biomarkers, ranged from 2 to 11; more concretely, MSP for ST 1 identification shows 2 specific peaks; MSP for ST 20 identification: 9 specific peaks; MSP for ST 22 and ST 36 identification: 11 specific peaks; MSP for ST 146 identification: 5 specific peaks; and MSP for ST 578 and ST 1086 identification: 3 specific peaks. Using the validation set (nine strains belonging to ST 22 and five to ST 1), MALDI-TOF assigned accurately the ST in 30 min per tested strain with a full match.

Conclusions

The ST of L. pneumophila can be identified and reported in few minutes directly from colonies grown on BCYE agar using MALDI-TOF.

中文翻译：

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一种用于嗜肺军团菌快速序列类型识别的新 MALDI-TOF 方法

背景

最近，MALDI-TOF 已成为细菌分型的快速工具。目的是评估基于 MALDI-TOF 的嗜肺军团菌分型是否可以获得与基于序列的分型 (SBT) 方法相同的区分能力。

方法

序列类型 (ST) 是从训练集中包含的 90 个菌株中获得的，并生成了一个基于主光谱图谱 (MSP) 的内部 MALDI-TOF 库，用于识别此类 ST。然后，我们的库通过三个程序进行验证：a) 创建树状图，b) 搜索每个 MSP 条目中仅存在的特定峰，以及 c) 分析由 14 个已知 ST 菌株组成的验证集。充分表征嗜肺军团菌属于 ST 36 的 ATCC 33152 用作对照菌株。结果：在训练集中，17 个菌株属于 ST 1、1 到 ST 20、63 到 ST 22、1 到 ST 146、6 到 ST 578 和 2 到 ST 1086。每个 MSPs 谱中都存在特定的峰，它们是被考虑的类型特异性生物标志物，范围从 2 到 11；更具体地说，用于 ST 1 识别的 MSP 显示了 2 个特定的峰；用于 ST 20 鉴定的 MSP：9 个特定峰；用于 ST 22 和 ST 36 鉴定的 MSP：11 个特定峰；用于 ST 146 鉴定的 MSP：5 个特定峰；和 MSP 用于 ST 578 和 ST 1086 鉴定：3 个特定峰。使用验证集（9 个属于 ST 22 的菌株和 5 个属于 ST 1 的菌株），MALDI-TOF 在 30 分钟内准确分配每个测试菌株的 ST，并完全匹配。

结论

L. pneumophila的 ST可以在几分钟内直接从使用 MALDI-TOF 在 BCYE 琼脂上生长的菌落中识别和报告。