Middleton J R, Fox L K, Gay J M, Tyler J W, Besser T E
Department of Veterinary Medicine and Surgery, University of Missouri, Columbia 65211, USA.
J Dairy Sci. 2002 May;85(5):1133-40. doi: 10.3168/jds.S0022-0302(02)74175-1.
The hypothesis tested was that there are differences in pathogenicity between strains of Staphylococcus aureus that cause bovine mastitis. Mammary quarter milk somatic cell count (SCC) and N-acetyl-beta-D-glucosaminidase (NAGase) activity were used as indicators of the pathogenicity of different strains of S. aureus that infect the bovine udder. Eight commercial dairy herds with a history of S. aureus in bulk tank milk cultures were studied. Initially, composite foremilk samples were collected from all lactating cattle in each herd and cultured for staphylococci. Subsequently, all cows with a coagulase-positive staphylococcal intramammary infection (IMI) at the initial sampling that were still present in the herd of origin had individual mammary quarter foremilk samples collected. Coagulase-positive staphylococcal isolates were confirmed as S. aureus using a commercial biotyping system. Staphylococcus aureus isolates were strain-typed using pulsed-field gel electrophoresis. Mammary quarter milk SCC and N-acetyl-beta-D-glucosaminidase activity were determined for each cow. The difference in mean somatic cell count and mean NAGase activity for mammary quarters infected with the same strain of S. aureus and for uninfected quarters on the same cow was calculated. One-way analysis of variance was used to assess differences between strains within a herd. Overall, no significant differences were found between strains, suggesting that the degree of udder parenchymal injury induced by S. aureus IMI is in general significantly affected by factors other than strain type.
所检验的假设是，引起牛乳腺炎的金黄色葡萄球菌菌株之间在致病性上存在差异。乳腺区牛奶体细胞计数（SCC）和N-乙酰-β-D-氨基葡萄糖苷酶（NAGase）活性被用作感染牛乳房的不同金黄色葡萄球菌菌株致病性的指标。对8个在散装罐牛奶培养物中有金黄色葡萄球菌病史的商业奶牛场进行了研究。最初，从每个牛群中的所有泌乳牛采集混合的前乳样本，并培养葡萄球菌。随后，对在初始采样时患有凝固酶阳性葡萄球菌乳房内感染（IMI）且仍在原牛群中的所有奶牛，采集其各个乳腺区的前乳样本。使用商业生物分型系统将凝固酶阳性葡萄球菌分离株确认为金黄色葡萄球菌。通过脉冲场凝胶电泳对金黄色葡萄球菌分离株进行菌株分型。测定每头奶牛的乳腺区牛奶SCC和N-乙酰-β-D-氨基葡萄糖苷酶活性。计算感染同一株金黄色葡萄球菌的乳腺区与同一头奶牛未感染乳腺区的平均体细胞计数和平均NAGase活性的差异。采用单因素方差分析来评估牛群内不同菌株之间的差异。总体而言，未发现菌株之间存在显著差异，这表明金黄色葡萄球菌IMI引起的乳房实质损伤程度一般受菌株类型以外的因素显著影响。
