Akindolire Muyiwa Ajoke, Babalola Olubukola Oluranti, Ateba Collins Njie
Department of Biological Sciences, School of Environmental and Health Sciences, Faculty of Agriculture, Science and Technology, North-West University, Mmabatho, Mafikeng Campus, South Africa.
Food Security and Safety Niche Area, Faculty of Agriculture, Science and Technology, North-West University, Mmabatho, Mafikeng 2735, South Africa.
Int J Environ Res Public Health. 2015 Aug 25;12(9):10254-75. doi: 10.3390/ijerph120910254.
The aim of this study was to investigate the occurrence, antibiotic susceptibility profiles, and virulence genes determinants of S. aureus isolated from milk obtained from retail outlets of the North-West Province, South Africa. To achieve this, 200 samples of raw, bulk and pasteurised milk were obtained randomly from supermarkets, shops and some farms in the North-West Province between May 2012 and April 2013. S. aureus was isolated and positively identified using morphological (Gram staining), biochemical (DNase, catalase, haemolysis and rapid slide agglutination) tests, protein profile analysis (MALDI-TOF mass spectrometry) and molecular (nuc specific PCR) methods. The antimicrobial resistance profiles of the isolates were determined using the phenotypic agar diffusion method. Genes encoding enterotoxins, exfoliative toxins and collagen adhesins were also screened using PCR. Among all the samples examined, 30 of 40 raw milk samples (75%), 25 of 85 bulk milk samples (29%) and 10 of 75 pasteurised milk samples (13%) were positive for S. aureus. One hundred and fifty-six PCR-confirmed S. aureus isolates were obtained from 75 contaminated milk samples. A large proportion (60%-100%) of the isolates was resistant to penicillin G, ampicillin, oxacillin, vancomycin, teicoplanin and erythromycin. On the contrary, low level resistance (8.3%-40%) was observed for gentamicin, kanamycin and sulphamethoxazole. Methicillin resistance was detected in 59% of the multidrug resistant isolates and this was a cause for concern. However, only a small proportion (20.6%) of these isolates possessed PBP2a which codes for Methicillin resistance in S. aureus. In addition, 32.7% of isolates possessed the sec gene whereas the sea, seb sed, see, cna, eta, etb genes were not detected. The findings of this study showed that raw, bulk and pasteurised milk in the North-West Province is contaminated with toxigenic and multi-drug resistant S. aureus strains. There is a need to implement appropriate control measures to reduce contamination as well as the spread of virulent S. aureus strains and the burden of disease in humans.
本研究旨在调查从南非西北省零售网点获取的牛奶中分离出的金黄色葡萄球菌的发生率、抗生素敏感性概况及毒力基因决定因素。为此,于2012年5月至2013年4月期间,从西北省的超市、商店及一些农场随机采集了200份生乳、散装乳和巴氏杀菌乳样本。采用形态学(革兰氏染色)、生化(DNA酶、过氧化氢酶、溶血及快速玻片凝集)试验、蛋白质谱分析(基质辅助激光解吸电离飞行时间质谱)及分子(nuc特异性PCR)方法分离并阳性鉴定金黄色葡萄球菌。采用表型琼脂扩散法测定分离株的抗菌药物耐药谱。还使用PCR筛选编码肠毒素、剥脱毒素和胶原黏附素的基因。在所有检测样本中,40份生乳样本中有30份(75%)、85份散装乳样本中有25份(29%)以及75份巴氏杀菌乳样本中有10份(13%)金黄色葡萄球菌检测呈阳性。从75份受污染的牛奶样本中获得了156株经PCR确认的金黄色葡萄球菌分离株。很大比例(60%-100%)的分离株对青霉素G、氨苄西林、苯唑西林、万古霉素、替考拉宁和红霉素耐药。相反,观察到庆大霉素、卡那霉素和磺胺甲恶唑的低水平耐药率(8.3%-40%)。在59%的多重耐药分离株中检测到耐甲氧西林,这令人担忧。然而,这些分离株中只有一小部分(20.6%)拥有编码金黄色葡萄球菌耐甲氧西林的PBP2a。此外,32.7%的分离株拥有sec基因,而未检测到sea、seb、sed、see、cna、eta、etb基因。本研究结果表明,西北省的生乳、散装乳和巴氏杀菌乳受到产毒和多重耐药金黄色葡萄球菌菌株的污染。有必要实施适当的控制措施,以减少污染以及毒性金黄色葡萄球菌菌株的传播和人类疾病负担。