Zecconi Alfonso, Binda Enrica, Borromeo Vitaliano, Piccinini Renata
Department of Animal Pathology, Hygiene and Public Health, Università degli Studi di Milano Via Celoria 10, 20133 Milano, Italy.
J Dairy Res. 2005 May;72(2):203-8. doi: 10.1017/s0022029905000841.
Staphylococcus aureus isolates produce several pathogenic factors. The combination of these products influences the pathogenic role of different isolates, but their specific effects are well known in the pathogenesis of udder infections. This study focused on the association of polymorphism of the coagulase gene, protein A gene, collagen-binding protein gene, and of fibrinogen-binding protein gene on somatic cell count (SCC) and on Staph. aureus growth rate. Fifty Staph. aureus isolates from 13 dairy cow herds, located in seven different provinces, were considered. The results showed a low frequency of cna gene, similar to the one observed in human isolates. Meanwhile, the high frequency of efb gene indirectly confirmed the role of this factor in bacterial pathogenesis, being associated with adhesion to epithelia. The association of these two single genes with SCC and growth rate showed to be not significant. The polymorphism of spa gene was confirmed to be significantly associated with inflammatory response and growth rate, albeit with a pattern different from the one suggested for human isolates. Sorting of isolates based on the clusters obtained by combining polymorphisms of spa and coa genes and the presence of cna and efb genes, showed that a single cluster (cluster V) was prevalent in the different herds and provinces, while the other six clusters identified were widely spread among the remaining 60% of the isolates. Results showed that clusters VI and VII had significantly higher growth rates at 3, 4, and 6 h in comparison with the other clusters. Meanwhile, quarters infected with these strains showed significantly lower SCC levels. The frequency of isolates from cluster V, suggested that they should possess pathogenic factors increasing their invasiveness, even if in the presence of a stronger inflammatory response. These results indirectly confirm previous findings on the different interactions between isolates and the udder immune system. They also suggest that isolates with higher growth rates and inducing a lower inflammatory response have better chances to spread among the herd. The relatively simple genomic method proposed in this study could be applied by an increasing number of diagnostic laboratories and could be useful in studying the epidemiology of Staph. aureus intra-mammary infections in dairy herds when collecting data from the field.
金黄色葡萄球菌分离株会产生多种致病因子。这些产物的组合会影响不同分离株的致病作用，但其具体作用在乳房感染的发病机制中是众所周知的。本研究聚焦于凝固酶基因、蛋白A基因、胶原结合蛋白基因和纤维蛋白原结合蛋白基因的多态性与体细胞计数（SCC）以及金黄色葡萄球菌生长速率之间的关联。研究考虑了来自七个不同省份13个奶牛群的50株金黄色葡萄球菌分离株。结果显示cna基因的频率较低，与在人类分离株中观察到的情况相似。同时，efb基因的高频率间接证实了该因子在细菌致病过程中的作用，它与上皮细胞黏附有关。这两个单基因与SCC和生长速率之间的关联并不显著。spa基因的多态性被证实与炎症反应和生长速率显著相关，尽管其模式与人类分离株所提示的不同。根据通过结合spa和coa基因的多态性以及cna和efb基因的存在所获得的聚类对分离株进行分类，结果表明单个聚类（聚类V）在不同牛群和省份中普遍存在，而鉴定出的其他六个聚类广泛分布于其余60%的分离株中。结果表明，与其他聚类相比，聚类VI和VII在3小时、4小时和6小时时的生长速率显著更高。同时，感染这些菌株的乳腺区显示出显著更低的SCC水平。聚类V分离株的频率表明，即使存在更强的炎症反应，它们也应具有增加其侵袭性的致病因子。这些结果间接证实了先前关于分离株与乳房免疫系统之间不同相互作用的研究发现。它们还表明，生长速率较高且诱导较低炎症反应的分离株在牛群中传播的机会更大。本研究中提出的相对简单的基因组方法可被越来越多的诊断实验室应用，并且在从现场收集数据时，可用于研究奶牛群中金黄色葡萄球菌乳房内感染的流行病学。
