Staphylococcus aureus is one of the most important pathogens causing mastitis in cattle, and it is responsible for economic losses in dairy herds worldwide. The PCR amplification of the 16S-23S rRNA intergenic spacer (ribosomal spacer PCR, RS-PCR) allows a rapid classification of the strains in genotypes and genotypic clusters (CL), which are characterized by different epidemiological and clinical properties. Both RS-PCR and multi-locus sequence typing (MLST) were performed on strains isolated from bovine bulk tank milk (BTM) collected from dairy herds located in the Lombardy region (northern Italy), to outline the distribution of Staph. aureus genotypes in this geographical area. Out of 844 examined samples, 398 were positive for Staph. aureus, with a variable count (cfu/mL) Up to 8 colonies from each sample were genotyped. A total of 1,101 Staph. aureus strains were analyzed with RS-PCR, and only a selection of them (n = 86), in relation to their frequency and geographical origin, underwent MLST. This study revealed 8 major genotypic clusters (CLB, CLC, CLR, CLS, CLI, CLF, CLAO, and CLZ), of which Staph. aureus CLB (29.3%) was the most common. Samples of BTM positive for CLB had a Staph. aureus cfu/mL count significantly higher than the non-CLB positive ones. Our MLST analysis showed genotypes already known as bovine-associated in literature, such as clonal complexes CC8, CC97, and CC151. The same selection of 86 strains was also analyzed for the presence of the adlb gene, which was recently proposed as a possible marker of contagiousness. Most Staph. aureus belonging to CLB or CC8 carried the adlb gene (85%), whereas this gene was detected in only 9% of non-CLB strains (CLAA, CLBI, CLBJ, CLS). In conclusion, the present study confirms that Staph. aureus CLB, which is recognized as a contagious genotype, is a particularly relevant agent of intramammary infection in dairy cows in Lombardy, and indirectly supports the idea that adlb can be a possible marker of contagiousness of isolates.

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简短交流：伦巴第（意大利北部）奶牛散装罐装牛奶中的金黄色葡萄球菌的表征。

金黄色葡萄球菌是引起牛乳腺炎的最重要病原体之一，它是造成全球奶牛场经济损失的原因。通过16S-23S rRNA基因间隔子的PCR扩增（核糖体间隔PCR，RS-PCR），可以根据基因型和基因型簇（CL）对菌株进行快速分类，其特征是具有不同的流行病学和临床特性。RS-PCR和多位点序列分型（MLST）均对从位于伦巴第大区（意大利北部）的奶牛场采集的牛散装牛奶（BTM）分离的菌株进行，以概述葡萄球菌的分布。该地理区域的金黄色葡萄球菌基因型。在844个检查样本中，有398个葡萄球菌阳性。对金黄色葡萄球菌进行计数（cfu / mL），对每个样品进行多达8个菌落的基因分型。共有1,101个Staph。用RS-PCR分析金黄色葡萄球菌菌株，仅针对其频率和地理来源对其中的一部分（n = 86）进行了MLST试验。这项研究揭示了8个主要的基因型簇（CLB，CLC，CLR，CLS，CLI，CLF，CLAO和CLZ），其中有葡萄球菌。最常见的是金黄色CLB（29.3％）。对CLB呈阳性的BTM样本具有葡萄球菌。金黄色葡萄球菌的cfu / mL计数明显高于非CLB阳性的。我们的MLST分析显示了文献中已被称为牛相关基因型，例如克隆复合物CC8，CC97和CC151。还分析了相同选择的86个菌株的adlb基因的存在，该基因最近被提议作为可能的传染性标记。大多数葡萄球菌。属于CLB或CC8的金黄色葡萄球菌带有adlb基因（85％），而只有9％的非CLB菌株（CLAA，CLBI，CLBJ，CLS）。总之，本研究证实了葡萄球菌。金黄色葡萄球菌CLB是公认的传染性基因型，是伦巴第地区奶牛乳房内感染的一个特别相关的因素，并间接支持adlb可能是分离株传染性的可能标志的观点。