Food Science and Nutrition Department, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia; Food Science and Nutrition Department, Faculty of Home Economics, Helwan University, P.O. Box 11611, Cairo, Egypt.
Food Science and Nutrition Department, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia.
J Dairy Sci. 2020 Jul;103(7):5947-5963. doi: 10.3168/jds.2019-17631. Epub 2020 Apr 29.
Staphylococcus aureus is a significant opportunistic pathogen in humans, dairy cattle, and camels. The presence of antibiotic-resistant and heat-resistant bacteria in camel milk has become a potential public health issue. The phenotypic and molecular characterization of methicillin-resistant staphylococcal strains recovered from pasteurized camel milk distributed in retail markets of Saudi Arabia was assessed. A total of 100 samples were collected between March and May 2017. Out of the 20 S. aureus isolates that were recovered from the pasteurized camel milk, 10 were found to be resistant to cefoxitin (30 µg) and, thus, were designated as methicillin-resistant strains. The resistance ratio of methicillin-resistant S. aureus isolates for a different class of antibiotics was determined by performing the antimicrobial susceptibility test and was estimated to be approximately 60%. Polymerase chain reaction assay was performed to amplify the methicillin-resistant gene mecA, and furthermore, nucleotide sequencing was performed to detect and verify the presence of methicillin-resistant strains. Upon sequencing the putative S. aureus methicillin-resistant strains, we obtained 96 to 100% similarity to the penicillin-binding protein 2a gene (mecA) of the S. aureus strain CS100. Moreover, the 10 methicillin-resistant S. aureus isolates were also identified to be heat resistant and were stable at temperatures up to 85°C for 60 s, with 3 isolates being heat resistant even at 90°C for 60 or 90 s. The mean decimal reduction time (D value) was 111 s for all the 10 isolates. No difference was observed in the profile of total protein between the 10 methicillin- and heat-resistant S. aureus isolates and the S. aureus strain ATCC 29737, which was determined by sodium dodecyl sulfate-PAGE analyses. Therefore, we could conclude that a relatively high percentage of the tested pasteurized camel milk samples were contaminated with S. aureus (20%) and methicillin- and heat-resistant S. aureus (10%).
金黄色葡萄球菌是人类、奶牛和骆驼的重要机会致病菌。骆驼奶中存在抗生素耐药和耐热细菌已成为潜在的公共卫生问题。本研究评估了从沙特阿拉伯零售市场销售的巴氏杀菌骆驼奶中分离出的耐甲氧西林金黄色葡萄球菌的表型和分子特征。2017 年 3 月至 5 月期间共采集了 100 份样本。从巴氏杀菌骆驼奶中分离出的 20 株金黄色葡萄球菌中有 10 株对头孢西丁（30µg）耐药，因此被鉴定为耐甲氧西林菌株。通过药敏试验测定了耐甲氧西林金黄色葡萄球菌对不同类别的抗生素的耐药率，估计约为 60%。采用聚合酶链反应（PCR）扩增耐甲氧西林基因 mecA，并对其进行核苷酸测序，以检测和验证耐甲氧西林菌株的存在。对疑似耐甲氧西林金黄色葡萄球菌进行测序后，我们获得了与金黄色葡萄球菌 CS100 青霉素结合蛋白 2a 基因（mecA）96%至 100%的相似性。此外，这 10 株耐甲氧西林金黄色葡萄球菌还被鉴定为耐热菌株，在 85°C 下稳定 60 秒，其中 3 株在 90°C 下稳定 60 秒或 90 秒。10 株耐甲氧西林金黄色葡萄球菌的平均十进制减少时间（D 值）均为 111 秒。通过十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS-PAGE）分析，10 株耐甲氧西林和耐热金黄色葡萄球菌与金黄色葡萄球菌 ATCC 29737 的总蛋白图谱没有差异。因此，我们可以得出结论，在所检测的巴氏杀菌骆驼奶样本中，有相对较高比例（20%）受到金黄色葡萄球菌污染，有 10%（10/100）受到耐甲氧西林和耐热金黄色葡萄球菌污染。
