Department of Biology, St. Cloud State University, Saint Cloud, MN, USA.
College of Veterinary Medicine, University of Minnesota, St. Paul, MN, USA.
J Microbiol Methods. 2021 Mar;182:106168. doi: 10.1016/j.mimet.2021.106168. Epub 2021 Feb 16.
MALDI-TOF is a chemistry analytical tool that has recently been deployed in the identification of microorganisms isolated from nosocomial environments. Its use in diagnostics has been extremely advantageous in terms of cost effectiveness, sample preparation easiness, turn-around time and result analysis accessibility. In the dairy industry, where mastitis causes great financial losses, a rapid diagnostic method such as MALDI-TOF could assist in the control and prevention program of mastitis, in addition to the sanitation and safety level of the dairy farms and processing facility. However, the diagnostic strengths and limitations of this test method require further understanding. In the present study, we prospectively compared MALDI-TOF MS to conventional 16S rDNA sequencing method for the identification of pathogens recovered from milk associated with clinical and subclinical bovine mastitis cases. Initially, 810 bacterial isolates were collected from raw milk samples over a period of three months. However, only the isolates (481) having both 16S rDNA sequencing and MALDI-TOF identification were included in the final phase of the study. Among the 481 milk isolates, a total of 26 genera (12 g-postive and 14 g-negative), including 71 different species, were taxonomically charecterized by 16S rDNA at the species level. Comparatively, MALDI-TOF identified 17 genera (9 g-positive and 8 g-negative) and 33 differernt species. Overall, 445 (93%) were putatively identified to the genus level by MALDI-TOF MS and 355 (74%) were identified to the species level, but no reliable identification was obtained for 16 (3.3%), and 20 (4.2%) discordant results were identified. Future studies may help to overcome the limitations of the MALDI database and additional sample preparation steps might help to reduce the number of discordances in identification. In conclusion, our results show that MALDI-TOF MS is a fast and reliable technique which has the potential to replace conventional identification methods for common mastitis pathogens, routinely isolated from raw milk. Thus it's adoption will strengthen the capacity, quality, and possibly the scope of diagnostic services to support the dairy industry.
基质辅助激光解吸电离飞行时间质谱（MALDI-TOF）是一种化学分析工具，最近已被用于鉴定医院环境中分离出的微生物。在诊断方面，其具有成本效益高、样本制备简单、周转时间短、结果易于分析等优势。在乳腺炎会造成巨大经济损失的乳品行业，MALDI-TOF 等快速诊断方法可以协助乳腺炎的控制和预防计划，以及提高奶牛场和加工设施的卫生和安全水平。然而，该检测方法的诊断优势和局限性需要进一步理解。在本研究中，我们前瞻性地比较了 MALDI-TOF MS 与传统 16S rDNA 测序方法，用于鉴定来自临床和亚临床乳腺炎病例牛奶中分离的病原体。最初，在三个月的时间内从原料奶样品中收集了 810 个细菌分离株。但是，只有具有 16S rDNA 测序和 MALDI-TOF 鉴定的分离株（481 个）被纳入研究的最后阶段。在 481 个牛奶分离株中，总共鉴定出 26 个属（12 个阳性菌属和 14 个阴性菌属），包括 71 个不同种，在种水平上通过 16S rDNA 进行了分类学描述。相比之下，MALDI-TOF 鉴定出 17 个属（9 个阳性菌属和 8 个阴性菌属）和 33 个不同种。总体而言，MALDI-TOF MS 对 445 株（93%）进行了假定的属水平鉴定，对 355 株（74%）进行了种水平鉴定，但有 16 株（3.3%）未得到可靠鉴定，有 20 株（4.2%）鉴定结果不一致。未来的研究可能有助于克服 MALDI 数据库的局限性，而额外的样本制备步骤可能有助于减少鉴定不一致的数量。总之，我们的研究结果表明，MALDI-TOF MS 是一种快速可靠的技术，有可能取代常规方法，用于常规分离自原料奶的常见乳腺炎病原体的鉴定。因此，其应用将提高乳品行业的能力、质量，并可能扩大诊断服务的范围。
