Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, United Kingdom.
J Dairy Sci. 2013 Aug;96(8):5129-45. doi: 10.3168/jds.2013-6741. Epub 2013 Jun 13.
Streptococcus uberis is an important cause of intramammary infection in dairy cattle. Strains of Strep. uberis appear to differ in their ability to cause disease based on previous epidemiological studies. We explored the pathogenicity of 2 strains of Strep. uberis, where one strain represented a putatively host-adapted type based on its ability to cause persistent infection and to spread from cow to cow in a lactating herd. This type was part of a clonal complex that is commonly associated with bovine mastitis. The other strain, which was isolated from a transient infection in a single animal in the same herd and did not belong to any known clonal complex, was selected as putatively nonadapted type. Cows (6 per strain) were experimentally challenged in a single hind quarter and the adjacent hind quarter was used as mock challenged control quarter. Both strains showed an equal ability to grow in the milk of challenge animals in vitro. All cows that were challenged with the putatively host-adapted strain developed clinical signs of mastitis, including fever and milk yield depression as well as elevated somatic cell count due to influx of polymorphonuclear leucocytes and lymphocytes. The cytokine response followed a specific order, with an increase in IL-1β, IL-6, and IL-8 levels at the time of first SCC elevation, followed by an increase in IL-10, IL-12p40, and tumor necrosis factor-α levels approximately 6h later. In 4 of 6 animals, IL-17A was detected in milk between 57 and 168 h postchallenge. The increase in IL-17A levels coincided with inversion of the prechallenge CD4(+)-to-CD8(+) T lymphocyte ratio, which was observed from 96 h postchallenge. This was followed by normalization of the CD4(+)-to-CD8(+) ratio due to continued increase of the CD8(+) concentration up to 312 h postchallenge. Spontaneous resolution of infection was observed in 5 animals and coincided with a measurable IL-17A response in 4 animals, suggesting that IL-17 may be involved in the resolution of intramammary infection. With the exception of minor elevation of IL-8 levels, no clinical, cytological, or immunological response was detected in quarters challenged with the nonadapted strain. The observed strain-specific pathogenicity was consistent across animals, implying that it is determined by pathogen factors rather than host factors.
停乳链球菌是奶牛乳腺炎的重要病原体。基于先前的流行病学研究，停乳链球菌菌株在致病能力方面似乎存在差异。我们探索了 2 株停乳链球菌的致病性，其中一株基于其持续感染和在泌乳牛群中从一头牛传播到另一头牛的能力，被认为是宿主适应型。该型属于与牛乳腺炎密切相关的克隆复合体的一部分。另一株从同一牛群中单个动物的短暂感染中分离出来，不属于任何已知的克隆复合体，被选为非适应型。每株菌选择 6 头奶牛进行单侧后乳区攻毒，对侧后乳区作为对照。在体外，两株菌在攻毒奶牛的奶中均表现出相同的生长能力。所有用宿主适应型菌株攻毒的奶牛均出现乳腺炎临床症状，包括发热和产奶量下降，由于多形核白细胞和淋巴细胞涌入，体细胞计数升高。细胞因子反应呈现出特定的顺序，在首次 SCC 升高时，IL-1β、IL-6 和 IL-8 水平增加，随后约 6h 后，IL-10、IL-12p40 和肿瘤坏死因子-α水平增加。在 6 头奶牛中，有 4 头在攻毒后 57 至 168h 检测到 IL-17A。IL-17A 水平的增加与攻毒后 96h 观察到的 CD4+向 CD8+T 淋巴细胞比值反转同时发生，这与持续增加的 CD8+浓度直至攻毒后 312h 有关。在 5 头奶牛中观察到感染自发缓解，其中 4 头在攻毒后检测到可测量的 IL-17A 反应，这表明 IL-17 可能参与了乳腺炎的缓解。除了 IL-8 水平的轻微升高外，用非适应型菌株攻毒的乳区未检测到临床、细胞学或免疫学反应。在不同动物中观察到的菌株特异性致病性是一致的，这表明它是由病原体因素而不是宿主因素决定的。
