Atalla Heba, Gyles Carlton, Jacob Christian L, Moisan Helene, Malouin François, Mallard Bonnie
Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
Foodborne Pathog Dis. 2008 Dec;5(6):785-99. doi: 10.1089/fpd.2008.0110.
Staphylococcus aureus is a common cause of bovine mastitis and foodborne and other diseases in humans. This study tested the hypothesis that small colony variants (SCVs) of S. aureus are implicated in chronic bovine mastitis. Six S. aureus isolates from foremilk samples from 11 chronically infected cows were investigated. Five isolates had typical morphology and were hemolytic and coagulase positive; one was a heterogeneous population of typical and SCV phenotype (tiny nonhemolytic colonies). In the presence of gentamicin, three of the previously typical S. aureus developed SCVs that were confirmed as S. aureus by biochemical and genetic analyses; these SCVs reverted to the typical form on antibiotic-free medium. The SCV isolate (Heba3231) from the heterogeneous population had a slow growth rate and prolonged lag phase and did not revert during 10 h of incubation. Transcriptional analysis showed that SCV Heba3231 had reduced expression of agr, hla, and coa and increased expression of indicators of fermentation pathways compared to the parent strain. Invasion of and persistence in a primary culture of bovine aortic endothelial cells (BAEC) showed that SCV Heba3231 had minimal deleterious effects, whereas the parent strain or the Newbould 305 strain caused severe damage. Recovery of the parent strain from BAEC yielded a mixture of the parent and SCV phenotypes. This study reports for the first time the isolation of S. aureus SCV from persistent bovine mastitis and suggests that SCV may be an important contributor to the prolonged survival of S. aureus in some cases of mastitis.
金黄色葡萄球菌是牛乳腺炎、食源性疾病及人类其他疾病的常见病因。本研究检验了金黄色葡萄球菌小菌落变异株（SCVs）与慢性牛乳腺炎有关的假说。对11头慢性感染奶牛的乳样中分离出的6株金黄色葡萄球菌进行了研究。5株分离株具有典型形态，溶血且凝固酶呈阳性；1株为典型和SCV表型的异质群体（微小非溶血菌落）。在庆大霉素存在的情况下，3株先前典型的金黄色葡萄球菌形成了SCVs，经生化和基因分析确认为金黄色葡萄球菌；这些SCVs在无抗生素培养基上又恢复为典型形态。来自异质群体的SCV分离株（Heba3231）生长速率缓慢且延滞期延长，在培养10小时期间未发生回复。转录分析表明，与亲本菌株相比，SCV Heba3231的agr、hla和coa表达降低，发酵途径指标的表达增加。在牛主动脉内皮细胞（BAEC）原代培养物中的侵袭和持续存在表明，SCV Heba3231的有害作用最小，而亲本菌株或Newbould 305菌株则造成严重损伤。从BAEC中回收亲本菌株得到亲本和SCV表型的混合物。本研究首次报道了从持续性牛乳腺炎中分离出金黄色葡萄球菌SCV，并表明SCV可能是金黄色葡萄球菌在某些乳腺炎病例中长时间存活的重要因素。
