German Federal Institute for Risk Assessment (BfR), Department Biological Safety, National Reference Laboratory for coagulase-positive staphylococci including Staphylococcus aureus, PO Box 126942, 10609 Berlin, Germany; Central Veterinary Research Institute, PO Box 33980, Lusaka, Zambia; University of Zambia (UNZA), School of Veterinary Medicine, PO Box 32379, Lusaka, Zambia.
University of Zambia (UNZA), School of Veterinary Medicine, PO Box 32379, Lusaka, Zambia.
Int J Food Microbiol. 2022 Aug 16;375:109737. doi: 10.1016/j.ijfoodmicro.2022.109737. Epub 2022 May 21.
Staphylococcus aureus is an important opportunistic pathogen of both humans and animals. It can cause several diseases, including mastitis, as well as food poisoning by production of heat-stable enterotoxins in food. The aim of this study was to determine the prevalence of S. aureus and the diversity of strains circulating in the Zambian dairy value chain, which have not been studied in detail before. Three provinces were covered by the study (Lusaka, Southern, and Western) and almost 2000 samples along the dairy value chain, covering both the informal and formal market sectors, were taken at two time points (dry and wet season), with a special focus on raw milk. Nearly 300 presumptive S. aureus isolates were confirmed by MALDI-TOF MS and real-time PCR. Raw milk from traditional and smallholder farms was widely contaminated with S. aureus; prevalence was 33-46% depending on the study province. Raw milk from milk collection centres, informal traders, traditional market sellers, and processors were also frequently contaminated with S. aureus. In addition, S. aureus was detected in several milk bucket swabs and nasal and hand swabs of milkers. From industrially processed (heat-treated) milk and dairy products, no S. aureus was isolated. Methicillin-resistant S. aureus (MRSA) were not detected, but around 10% of the S. aureus isolates carried lukS-PV, a marker gene for the virulence factor Pantone-Valentine leucocidin (PVL), which has been associated with severe diseases in human. Molecular typing identified a total of 44 spa types including 13 novel types: t18396, t18397, t18398, t18399, t18400, t18402, t18416, t20459, t20460, t20461, t20462, t20463, and t20464. Furthermore, 12 novel multi-locus sequence types were identified: ST7012, ST7100, ST7101, ST7177, ST7291, ST7304, ST7305, ST7344, ST7596, ST7597, ST7598, and ST7599, of which ST7012, ST7177, and ST7596 fall into the bovine-associated clonal linage CC97. The spa types t084, t267, t355, and the novel type t20464 were common in all three study provinces. The predominant spa type varied depending on the province. Whole genome sequencing (WGS) and core genome multi-locus sequence typing (cgMLST) indicates transmission of strains along the Zambian dairy chain with possible persistence in the chain over time. cgMLST also revealed a very close relatedness between some isolates from milkers and from raw milk or milk buckets. The high prevalence and wide spa type diversity of S. aureus, as well as possible direct or indirect transmission of (potentially highly virulent) S. aureus to humans along the Zambian dairy value chain, are of public health concern, particularly as milk and milk products are often consumed raw by the Zambian population.
金黄色葡萄球菌是人类和动物的重要机会致病菌。它可以引起多种疾病，包括乳腺炎，以及通过在食物中产生耐热肠毒素而引起的食物中毒。本研究旨在确定赞比亚乳业价值链中金黄色葡萄球菌的流行情况和菌株的多样性，此前尚未对此进行详细研究。该研究覆盖了三个省（卢萨卡、南部和西部），在两个时间点（旱季和雨季），在乳业价值链的各个环节，包括非正式和正式市场部门，采集了近 2000 个样本，特别关注生奶。通过 MALDI-TOF MS 和实时 PCR 确认了近 300 个推定的金黄色葡萄球菌分离株。传统和小农户的生奶受到金黄色葡萄球菌的广泛污染；根据研究省份的不同，患病率为 33-46%。来自奶收集中心、非正规贸易商、传统市场销售商和加工商的生奶也经常受到金黄色葡萄球菌的污染。此外，在几个奶桶拭子和挤奶工的鼻腔和手部拭子中也检测到了金黄色葡萄球菌。未从工业加工（热处理）牛奶和乳制品中分离出耐甲氧西林金黄色葡萄球菌（MRSA），但约 10%的金黄色葡萄球菌分离株携带 lukS-PV，这是一种与人类严重疾病相关的杀白细胞素潘通-瓦伦丁素（PVL）的毒力基因。分子分型共鉴定出 44 种 spa 型，包括 13 种新类型：t18396、t18397、t18398、t18399、t18400、t18402、t18416、t20459、t20460、t20461、t20462、t20463 和 t20464。此外，还鉴定出 12 种新的多位点序列类型：ST7012、ST7100、ST7101、ST7177、ST7291、ST7304、ST7305、ST7344、ST7596、ST7597、ST7598 和 ST7599，其中 ST7012、ST7177 和 ST7596 属于牛相关克隆谱系 CC97。spa 型 t084、t267、t355 和新型 t20464 在三个研究省份均很常见。主要 spa 型因省份而异。全基因组测序（WGS）和核心基因组多位点序列分型（cgMLST）表明，菌株沿着赞比亚乳业链传播，随着时间的推移，菌株可能在链中持续存在。cgMLST 还表明，挤奶工的一些分离株与生奶或奶桶中的分离株之间存在非常密切的关系。金黄色葡萄球菌的高流行率和广泛的 spa 型多样性，以及金黄色葡萄球菌沿着赞比亚乳业价值链直接或间接（可能高度致病）传播给人类的可能性，引起了公共卫生关注，特别是因为牛奶和奶制品经常被赞比亚人食用生的。
