Staphylococcus aureus (S. aureus) is the most important pathogen involved in bovine mastitis in dairy production. S. aureus produces a spectrum of extracellular protein toxins and virulence factors which are thought to contribute to the pathogenicity of the organism. The aim of this work was to isolate and molecular characterize S. aureus associated with bovine subclinical mastitis in the central part of Ethiopia. A total of 265 lactating dairy cows from various dairy farms in four different geographical locations were screened by the California mastitis test (CMT) for bovine subclinical mastitis. One hundred thirty CMT-positive milk samples were collected and transported to the laboratory. Different biochemical tests and polymerase chain reaction (PCR) were used for the identification of S. aureus isolates. Finally, PCR was performed for molecular detection of virulence genes. From a total of 265 lactating dairy cows screened, 49% (n = 130) were positive for bovine subclinical mastitis. One hundred thirty mastitic milk samples were subjected to bacterial culturing, and one hundred (76%) S. aureus isolates were identified based on phenotypic characters. Sixty-eight confirmed S. aureus isolates were obtained using PCR. The confirmed S. aureus isolates were tested for six virulence genes (tsst-1, hlb, eta, sea, clfA, and icaD) using PCR. Of the six virulence genes screened from all the isolates, only two (clfA and eta) were detected in the isolates. Out of 68 isolates, 25% and 22% were possessed the eta and clfA genes, respectively. The presence of Staphylococcus aureus having virulence genes (eta and clfA) revealed that mastitis is a major concern nowadays affecting animal health, milk quality, and yield. Further genomic study of these isolates will provide broad new insights on virulence.

中文翻译：

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埃塞俄比亚中部牛亚临床乳腺炎分离的金黄色葡萄球菌毒力因子的分子特征

金黄色葡萄球菌 (S. aureus) 是奶牛生产中与牛乳腺炎有关的最重要病原体。金黄色葡萄球菌产生一系列细胞外蛋白质毒素和毒力因子，被认为有助于生物体的致病性。这项工作的目的是分离和分子表征与埃塞俄比亚中部的牛亚临床乳腺炎相关的金黄色葡萄球菌。通过加利福尼亚乳腺炎测试 (CMT) 对来自四个不同地理位置的各个奶牛场的总共 265 头泌乳奶牛进行了牛亚临床乳腺炎筛查。收集了 130 份 CMT 阳性牛奶样品并运送到实验室。不同的生化测试和聚合酶链反应 (PCR) 用于鉴定金黄色葡萄球菌分离株。最后，PCR用于毒力基因的分子检测。从总共筛选的 265 头泌乳奶牛中，49%（n = 130）对牛亚临床乳腺炎呈阳性​​。对 130 份乳糜泻样品进行细菌培养，根据表型特征鉴定出 100 株 (76%) 金黄色葡萄球菌分离株。使用 PCR 获得了 68 株经确认的金黄色葡萄球菌分离株。使用 PCR 对确认的金黄色葡萄球菌分离株进行了六种毒力基因（tsst-1、hlb、eta、sea、clfA 和 icaD）测试。在从所有分离株中筛选出的六个毒力基因中，在分离株中仅检测到两个（clfA 和 eta）。在 68 个分离株中，分别有 25% 和 22% 具有 eta 和 clfA 基因。具有毒力基因（eta 和 clfA）的金黄色葡萄球菌的存在表明，乳腺炎是当今影响动物健康、牛奶质量和产量的主要问题。对这些分离株的进一步基因组研究将为毒力提供广泛的新见解。