Department of Veterinary Medicine, University of Sassari, Sassari, Italy.
Foodborne Pathog Dis. 2013 Apr;10(4):310-5. doi: 10.1089/fpd.2012.1356. Epub 2013 Mar 4.
The presence of Staphylococcus aureus in raw milk can represent a potential threat to human health, due to the introduction of pathogenic strains into dairy food supply chain. The present study was performed to investigate the genetic variation among S. aureus strains isolated from bulk tank goat's milk. The virulence profiles were also assessed to link the isolates with the potential source of milk contamination. A population study was performed on 60 strains using distance-based methods such as pulsed-field gel electrophoresis (PFGE), and the output was analyzed using Structure statistical software (University of Chicago; http://pritch.bsd.uchicago.edu/structure.html ). This Bayesian clustering model tool allows one to assign individuals into a population with no predefined structure. In order to assess partition of genetic variability among isolates, groups obtained by Structure were also investigated using analysis of molecular variance. S. aureus was recovered in 60 out of 78 samples (76.9%) collected from 26 farms. According to PFGE analysis, the strains were divided into 25 different pulsotypes and grouped into two main clusters. Restriction profiles, analyzed by Structure, allowed us to identify two distinct S. aureus genetic groups. Within each group, the strains showed a high coefficient of membership. A great part of genetic variability was attributable to within-groups variation. On the basis of the virulence profile, 45% of the isolates were linked to "animal" biovar, while 6.7% could be assigned to "human" biovar. Out of 60 strains, 27 were characterized by in vitro production of either enterotoxins A (5.0%), C (38.3%), or D (1.7%). The present study showed a high prevalence of bulk tank goat's milk contamination with S. aureus of animal origin. The presence in goat's milk of S. aureus strains able to produce enterotoxins and their potential introduction into dairy chain may represent a serious threat to human health.
金黄色葡萄球菌存在于生奶中可能对人类健康构成潜在威胁，因为致病菌株可能会被引入到乳制品供应链中。本研究旨在调查从散装奶山羊奶中分离的金黄色葡萄球菌菌株的遗传变异。还评估了这些分离株的毒力谱，以将其与牛奶污染的潜在来源联系起来。使用基于距离的方法（如脉冲场凝胶电泳（PFGE））对 60 株菌株进行了群体研究，并用 Structure 统计软件（芝加哥大学；http://pritch.bsd.uchicago.edu/structure.html）对结果进行了分析。这种贝叶斯聚类模型工具允许将个体分配到没有预定义结构的群体中。为了评估分离株之间遗传变异的分配，还使用结构分析对分子方差进行了分析。从 26 个农场采集的 78 个样本中有 60 个（76.9%）回收了金黄色葡萄球菌。根据 PFGE 分析，这些菌株被分为 25 种不同的脉冲型，并分为两个主要聚类。结构分析的限制图谱使我们能够识别出两种不同的金黄色葡萄球菌遗传群。在每个群内，菌株显示出高的成员系数。大部分遗传变异归因于群内变异。根据毒力谱，45%的分离株与“动物”生物型相关，而 6.7%的分离株可归类为“人类”生物型。在 60 株菌株中，有 27 株表现出体外产肠毒素 A（5.0%）、C（38.3%）或 D（1.7%）的特性。本研究表明，散装奶山羊奶中金黄色葡萄球菌污染的发生率很高，且污染的金黄色葡萄球菌主要来源于动物。山羊奶中存在能够产生肠毒素的金黄色葡萄球菌菌株及其可能被引入乳制品供应链，这可能对人类健康构成严重威胁。
