Kudirkiene Egle, Welker Martin, Knudsen Nanna R, Bojesen Anders M
Department of Veterinary Disease Biology, University of Copenhagen, Stigbøjlen 4, 1870 Frederiksberg C, Denmark.
BioMérieux SA, Unit Microbiology, R&D Microbiology, La Balme Les Grottes 38390, France.
Syst Appl Microbiol. 2015 Jul;38(5):315-22. doi: 10.1016/j.syapm.2015.02.010. Epub 2015 Apr 23.
Streptococcus equi includes very important animal and human pathogens. S. equi subsp. equi (SEE) is a highly pathogenic equine specific subspecies, while S. equi subsp. zooepidemicus (SEZ) and S. equi subsp. ruminatorum are opportunistic pathogens of various animal species and humans. Due to great phenotypic and sequence similarity between three subspecies their discrimination remains difficult. In this study, we aimed to design and validate a novel, Superspectra based, MALDI-TOF MS approach for reliable, rapid and cost-effective identification of SEE and SEZ, the most frequent S. equi subspecies in horses. Superspectra created in this study enabled correct identification of 86 strains belonging to different subspecies of S. equi, isolated from various hosts, infection sites and years. In general, higher average identification accuracy was achieved for SEE (99.0±3.0%) than for SEZ (93.3±7.5%). This result may be attributed to the highly clonal population structure of SEE, as opposed to the diversity of SEZ seen in horses. Importantly strains with atypical colony appearance both within SEE and SEZ did not affect correct identification of the strains by MALDI-TOF MS. Atypical colony variants are often associated with a higher persistence or virulence of S. equi, thus their correct identification using the current method strengthens its potential use in routine clinical diagnostics. In conclusion, reliable identification of S. equi subspecies was achieved by combining a MALDI-TOF MS method with spectra analyses using the SARAMIS database. Additionally, first results on subtyping of SEZ indicated that a more refined discrimination, for example for epidemiological surveys, may be possible.
马链球菌包含非常重要的动物和人类病原体。马链球菌马亚种（SEE）是一种高致病性的马属特异性亚种，而马链球菌兽疫亚种（SEZ）和马链球菌反刍动物亚种是各种动物和人类的机会性病原体。由于这三个亚种在表型和序列上有很大的相似性，对它们进行区分仍然很困难。在本研究中，我们旨在设计并验证一种基于超光谱的新型基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）方法，用于可靠、快速且经济高效地鉴定SEE和SEZ，这两种是马中最常见的马链球菌亚种。本研究中创建的超光谱能够正确鉴定从不同宿主、感染部位和年份分离出的属于马链球菌不同亚种的86株菌株。总体而言，SEE的平均鉴定准确率（99.0±3.0%）高于SEZ（93.3±7.5%）。这一结果可能归因于SEE高度克隆的种群结构，与之形成对比的是在马中观察到的SEZ的多样性。重要的是，SEE和SEZ中具有非典型菌落外观的菌株并不影响MALDI-TOF MS对菌株的正确鉴定。非典型菌落变体通常与马链球菌更高的持续性或毒力相关，因此使用当前方法对它们进行正确鉴定增强了其在常规临床诊断中的潜在应用价值。总之，通过将MALDI-TOF MS方法与使用SARAMIS数据库的光谱分析相结合，实现了对马链球菌亚种的可靠鉴定。此外，关于SEZ分型的初步结果表明，例如对于流行病学调查，可能实现更精细的区分。
