Department of Veterinary Medicine, University of Milan, Via Celoria 10, 20133, Milan, Italy.
Department of Agricultural and Environmental Sciences - Production, Land, Agroenergy, University of Milan, Via Celoria 2, 20133, Milan, Italy.
Vet Microbiol. 2018 Dec;227:29-33. doi: 10.1016/j.vetmic.2018.10.021. Epub 2018 Oct 27.
Methicillin-resistant S. aureus (MRSA) lineages have become major responsible of healthcare- and community-associated infections in human population. Bovine MRSA are sporadically detected in the dairy herd, but its presence enhances the risk of zoonosis. Some lineages are able to lose the specific host tropism, being easily transmitted from animals to humans and vice-versa. The present study aims at clarifying the epidemiology of MRSA intramammary infections in a closed dairy herd, which was running a mastitis control program since years. Quarter milk samples were collected from all lactating cows once a week for 9 weeks and bacteriologically tested. At the end of the follow-up period, also a self-taken nasal swab of the milker was analysed. Three cows (12.5%) were MRSA positive, a fourth showed a transient infection and MRSA was isolated also from the milker's nose. Somatic cell counts of infected quarters fluctuated from 1000 to 1,800,000 cells/mL. The isolates were genotyped using DNA microarrays and identified as the epidemic UK-EMRSA-15 grouping in CC22. All strains carried the genes for β-lactam and macrolide resistance. The milker isolate differed from cow isolates mainly for the absence of the untruncated β-haemolysin and the presence of the immune evasion cluster. The milker had been volunteering in a nursing home since months, thus playing the role of MRSA vector into the herd. Our results showed the adaptive capacity of such MRSA to the bovine host. Therefore, we suggest that CC22-MRSA should be regarded as a potential cause of reverse zoonosis in dairy cattle herds.
耐甲氧西林金黄色葡萄球菌（MRSA）株系已成为人类中与医疗保健和社区相关感染的主要原因。牛源 MRSA 偶尔在奶牛群中被检测到，但它的存在增加了人畜共患病的风险。一些株系能够失去特定的宿主趋向性，容易从动物传播到人类，反之亦然。本研究旨在阐明一个封闭奶牛群中 MRSA 乳房感染的流行病学，该奶牛群多年来一直在运行乳腺炎控制计划。每周从所有泌乳牛采集一次奶样，共采集 9 周，并进行细菌学检测。在随访期结束时，还对挤奶工的鼻拭子进行了分析。3 头奶牛（12.5%）呈 MRSA 阳性，第 4 头呈短暂感染，MRSA 也从挤奶工的鼻子中分离出来。受感染乳区的体细胞计数从 1000 到 1800000 个细胞/ml 波动。使用 DNA 微阵列对分离株进行基因分型，并鉴定为 CC22 中的流行 UK-EMRSA-15 分组。所有菌株均携带β-内酰胺和大环内酯类耐药基因。与牛分离株相比，挤奶工分离株主要缺乏未截断的β-溶血素，且存在免疫逃逸簇。挤奶工自几个月前开始自愿在一家疗养院工作，因此在牛群中充当了 MRSA 的传播媒介。我们的结果表明，这种 MRSA 对牛宿主具有适应性。因此，我们建议将 CC22-MRSA 视为奶牛群中反向人畜共患病的潜在原因。
