Naushad Sohail, Naqvi S Ali, Nobrega Diego, Luby Christopher, Kastelic John P, Barkema Herman W, De Buck Jeroen
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada.
Canadian Bovine Mastitis and Milk Quality Research Network, St-Hyacinthe, Quebec, Canada.
mSystems. 2019 Mar 5;4(2). doi: 10.1128/mSystems.00098-18. eCollection 2019 Mar-Apr.
Non- staphylococci (NAS) are the most frequently isolated pathogens from intramammary infection (IMI) in dairy cattle. Virulence factors (VFs) and mechanisms by which NAS cause IMI are not fully known. Herein, we analyzed the distribution of 191 VFs in 441 genomes of 25 NAS species, after classifying VFs into functional categories: adherence ( = 28), exoenzymes ( = 21), immune evasion ( = 20), iron metabolism ( = 29), and toxins ( = 93). In addition to establishing VF gene profiles, associations of VF genes between and among functional categories were computed, revealing distinctive patterns of association among VFs for various NAS species. Associations were also computed for low, medium, and high somatic cell count (SCC) and clinical mastitis (CM) isolates, demonstrating distinctive patterns of associations for low SCC and CM isolates, but no differences between high SCC and CM isolates. To determine whether VF distributions had any association with SCC or CM, various clustering approaches, including complete linkages, Ward clustering, and t-distributed stochastic neighbor embedding, were applied. However, no clustering of isolates representing low SCC, medium SCC, or high SCC or CM was identified. Regression analysis to test for associations with individual VF functional categories demonstrated that each additional toxin and host immune evasion gene increased the odds of having high SCC or CM, although an overall increase in the number of VFs was not associated with increased SCC or occurrence of CM. In conclusion, we established comprehensive VF gene profiling, determined VF gene distributions and associations, calculated pathogenic potentials of all NAS species, and detected no clear link between VF genes and mastitis. Non- staphylococci (NAS) are the most frequently isolated pathogens from milk in dairy cattle worldwide. The virulence factors (VFs) and mechanisms by which these bacteria cause udder infection are not fully known. We determined the distribution and associations of 191 VFs in 25 NAS species and investigated the relationship between VFs and disease. Although the overall number of VFs was not associated with disease severity, increasing numbers of toxin and host immune evasion genes specifically were associated with more severe disease outcomes. These findings suggest that the development of disease and the interactions of VFs with the host are complex and determined by the interplay of genes rather than just the presence of virulence genes. Together, our results provide foundational genetic knowledge to other researchers to design and conduct further experiments, focusing on understanding the synergy between VFs and roles of individual NAS species in IMI and characterizing species-specific effects on udder health.
非葡萄球菌（NAS）是奶牛乳房内感染（IMI）中最常分离出的病原体。NAS导致IMI的毒力因子（VF）和机制尚未完全明确。在此，我们将191种VF分为功能类别（黏附[=28种]、外酶[=21种]、免疫逃避[=20种]、铁代谢[=29种]和毒素[=93种]）后，分析了25种NAS物种的441个基因组中191种VF的分布情况。除了建立VF基因谱外，还计算了功能类别之间和之内的VF基因关联，揭示了不同NAS物种VF之间独特的关联模式。还计算了低、中、高体细胞计数（SCC）和临床型乳房炎（CM）分离株的关联，显示低SCC和CM分离株有独特的关联模式，但高SCC和CM分离株之间无差异。为了确定VF分布是否与SCC或CM有任何关联，应用了各种聚类方法，包括完全连锁法、沃德聚类法和t分布随机邻域嵌入法。然而，未发现代表低SCC、中SCC或高SCC或CM的分离株聚类情况。对与各个VF功能类别关联的回归分析表明，每增加一个毒素和宿主免疫逃避基因，出现高SCC或CM的几率就会增加，尽管VF数量的总体增加与SCC增加或CM发生无关。总之，我们建立了全面的VF基因谱，确定了VF基因分布和关联，计算了所有NAS物种的致病潜力，未发现VF基因与乳房炎之间有明确联系。非葡萄球菌（NAS）是全球奶牛乳汁中最常分离出的病原体。这些细菌导致乳房感染的毒力因子（VF）和机制尚未完全明确。我们确定了25种NAS物种中191种VF的分布和关联，并研究了VF与疾病之间的关系。尽管VF的总数与疾病严重程度无关，但毒素和宿主免疫逃避基因数量的增加尤其与更严重的疾病结果相关。这些发现表明，疾病的发展以及VF与宿主的相互作用很复杂，是由基因的相互作用决定的，而不仅仅是毒力基因的存在。总之，我们的结果为其他研究人员提供了基础遗传学知识，以设计和开展进一步实验，重点是了解VF之间的协同作用以及各个NAS物种在IMI中的作用，并确定对乳房健康的物种特异性影响。
