German Federal Institute for Risk Assessment (BfR), Department of Biological Safety, 10589 Berlin, Germany.
Robert Koch Institute (RKI), 38855 Wernigerode, Germany.
J Dairy Sci. 2020 Dec;103(12):11806-11819. doi: 10.3168/jds.2020-18958. Epub 2020 Oct 9.
The objective of this study was to investigate the occurrence and distribution of methicillin-resistant Staphylococcus aureus (MRSA) on 20 German dairy farms. Farms were selected based on previous MRSA reports from phenotypic susceptibility testing of mastitis pathogens. Samples were collected from predefined groups of cows, young stock, farm personnel, and the environment. A high MRSA-positive test rate was detected in swab samples from milk-fed calves (22.7%; 46/203). In postweaning calves, the MRSA-positive test rate was 9.1% (17/187). From prefresh heifers, both nasal swabs and udder cleft swabs were collected if possible. Including both sample types, the MRSA-positive test rate in prefresh heifers was 13.0% (26/200). The positive test rate was 8.9% (17/191) in nasal swabs and 6.5% (11/170) in udder cleft swabs. In quarter milk samples (QMS), the MRSA-positive test rate was 2.9% (67/2347), and on cow level, 7.9% (47/597) of the dairy cows were affected. Among all cows included in this study, the geometric mean of somatic cell counts was higher in QMS that carried MRSA (345,000 cells/mL) in comparison to all QMS (114,000 cells/mL). No differences in parity or the affected mammary quarter position on the udder were observed among the 47 infected cows. Methicillin-resistant S. aureus was also detected in boot swab samples (dust), teat liners, and in suckers from automatic calf feeders. All isolates belonged to livestock-associated sequence type 398 and most common staphylococcal protein A (spa)-types were t011 and t034. Most isolates harbored the staphylococcal cassette chromosome mec (SCCmec)-type V, with the exception of some isolates with SCCmec-type IVa on 1 farm. Similar MRSA genotypes in samples from humans and dairy cows underline the possible zoonotic and reverse-zoonotic transmission of livestock-associated MRSA strains from dairy farms. Similar MRSA genotypes in pig and cattle barns were detected on only 1 of 5 farms that kept both cattle and pigs. Similar MRSA spa-types were detected in samples from different sources (dairy cows, young stock, environment, and humans), suggesting a possible contagious transmission on some of the farms. Sporadically, up to 3 different MRSA spa-types were detected in QMS from the respective farms. On MRSA-affected farms, improper milking hygiene procedures and elevated bulk-tank milk somatic cell counts (>250,000 cells/mL) were observed. The occurrence of livestock-associated MRSA ST398 in different samples from dairy farms, and especially in young calves, should be considered for future MRSA-monitoring programs and biosecurity guidelines.
本研究的目的是调查 20 家德国奶牛场中耐甲氧西林金黄色葡萄球菌（MRSA）的发生和分布情况。根据先前从乳腺炎病原体表型药敏试验中报告的 MRSA 情况，选择了这些农场。从预先确定的奶牛、幼畜、农场人员和环境群体中采集样本。从用牛奶喂养的小牛的拭子样本中检测到高阳性 MRSA 检测率（22.7%；46/203）。在断奶后小牛中，MRSA 阳性检测率为 9.1%（17/187）。对于后备奶牛，如果可能，会同时采集鼻拭子和乳房皱襞拭子。包括两种样本类型，后备奶牛的阳性检测率为 13.0%（26/200）。鼻拭子的阳性检测率为 8.9%（17/191），乳房皱襞拭子的阳性检测率为 6.5%（11/170）。在乳区奶样（QMS）中，MRSA 阳性检测率为 2.9%（67/2347），在奶牛水平上，47/597 头奶牛受到影响。在本研究中纳入的所有奶牛中，携带 MRSA 的 QMS 的体细胞计数几何平均值（345,000 个细胞/mL）高于所有 QMS（114,000 个细胞/mL）。在 47 头感染奶牛中，未观察到产仔数或乳房上受影响的乳区位置的差异。从靴式拭子样本（灰尘）、乳头衬里和自动犊牛喂养器的奶嘴中也检测到耐甲氧西林金黄色葡萄球菌。所有分离株均属于与牲畜相关的序列类型 398，最常见的葡萄球菌蛋白 A（spa）-型为 t011 和 t034。大多数分离株携带金黄色葡萄球菌盒式染色体 mec（SCCmec）-类型 V，除了 1 个农场的一些分离株具有 SCCmec-类型 IVa 。从人类和奶牛中分离到的 MRSA 基因型相似，这强调了从奶牛场传播与牲畜相关的 MRSA 菌株的可能人畜共患病和反向人畜共患病。在仅保留牛和猪的 5 个农场中的 1 个农场中，仅检测到猪舍和牛舍中相似的 MRSA 基因型。在不同来源（奶牛、幼畜、环境和人类）的样本中检测到相似的 MRSA spa-型，这表明在一些农场中可能存在传染性传播。在各自农场的 QMS 中，偶尔会检测到高达 3 种不同的 MRSA spa-型。在受 MRSA 影响的农场中，观察到挤奶卫生程序不当和奶罐体细胞计数升高（>250,000 个细胞/mL）。应考虑在未来的 MRSA 监测计划和生物安全指南中考虑从奶牛场的不同样本中分离出与牲畜相关的 MRSA ST398，特别是在幼畜中。
