Staphylococcus aureus is one of the most concerning mastitis-causing pathogens in dairy cattle. Using basic microbiological techniques, S. aureus is typically identified by colony characteristics and hemolysis on blood agar where isolates without hemolysis are typically considered to be coagulase-negative staphylococci (CNS) isolates. Herein, we present a decade-long case study where suspected S. aureus isolates from one Georgia dairy farm were further tested to confirm presumptive identification. Presumptive identification of bacterial growth from 222 mammary secretions from bred Holstein heifers and lactating cows was conducted at the time of collection. Presumptive identification of S. aureus on blood agar was based on observation of colony morphology, color, and presence or absence of a broad zone of incomplete hemolysis and a smaller zone of complete hemolysis at 48 h. Those without hemolysis were presumptively characterized as CNS. All isolates were further plated on mannitol salt agar and a coagulase test was performed. A positive for both of these tests together was deemed to be S. aureus. A selection of isolates was tested using API® Staph to biochemically confirm S. aureus identification. Data showed that 63.96% of isolates presumed to be CNS isolates were identified as S.aureus, 9.46% of isolates presumed to be CNS isolates were identified as coagulase-positive staphylococci (CPS) species (but not S. aureus), and 26.58% of samples that were presumed to be CNS isolates were identified correctly.

中文翻译：

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案例研究：牛乳腺炎病例中的非溶血性金黄色葡萄球菌分离物误诊为凝固酶阴性葡萄球菌

金黄色葡萄球菌是奶牛中最引起乳腺炎的致病菌之一。使用基本的微生物学技术，金黄色葡萄球菌通常通过菌落特征和血琼脂上的溶血来鉴定，其中不溶血的分离株通常被认为是凝固酶阴性葡萄球菌（CNS）分离株。在这里，我们提出了一个长达十年的案例研究，其中对来自乔治亚州一家奶牛场的疑似金黄色葡萄球菌进行了进一步测试，以确认推定的身份。在收集时，从繁殖的荷斯坦小母牛和泌乳母牛的222个乳腺分泌物中推测细菌生长。金黄色葡萄球菌的推定鉴定对血琼脂的观察是基于在48小时观察到的菌落形态，颜色以及是否存在不完全溶血的宽区域和较小的完全溶血的区域。那些没有溶血的患者被假定为中枢神经系统。将所有分离物进一步铺在甘露醇盐琼脂上，并进行凝固酶测试。这两个测试的阳性结果一起被认为是金黄色葡萄球菌。使用金黄色葡萄球菌（Staph）对分离株的选择进行了测试，以生物化学方法确认金黄色葡萄球菌的鉴定。数据表明，分离的63.96％推定为CNS分离物鉴定为S.黄色葡萄球菌，推测是CNS分离物分离物的9.46％被鉴定为凝固酶阳性的葡萄球菌（CPS）物种（但不是金黄色葡萄球菌），并正确鉴定了26.58％的假定为CNS分离株的样品。