Classical enterotoxins of coagulase-positive Staphylococcus aureus isolates from raw milk and products for raw milk cheese production in Ireland
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- Hunt, K., Schelin, J., Rådström, P. et al. Dairy Sci. & Technol. (2012) 92: 487. doi:10.1007/s13594-012-0067-4
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Toxin-producing Staphylococcus aureus can be present in raw milk and therefore in cheese made from raw milk. To determine the number and type of toxin producers in raw milk used for raw milk cheese production in Ireland, 117 samples of raw milk and related products from five raw milk suppliers, to four raw milk cheesemakers in the South of Ireland, were analysed for coagulase positive S. aureus. Enumeration, using ISO 688-2 and plating on Baird Parker Rabbit Plasma Fibrinogen selective agar showed samples were within limits set by EC regulations. Isolates (151 from 81 positive samples) were characterised for production of staphylococcal enterotoxins (SEs) SEA, SEB, SEC and SED by reverse passive latex agglutination (SET-RPLA) and by multiplex polymerase chain reaction for the sea, seb, sec, sed and see genes. The results showed 83.2% of the isolates did not contain the se genes or the toxin producing capability tested for. From only one supplier, 26 isolates contained the sec gene and produced SEC. Within these 26 isolates, there were only two PFGE types. One SEC-producing isolate showed no toxin production when grown in sterile 10% reconstituted skim milk at 10 °C and 12 °C for 96 and 74 h, respectively. Low concentrations of SEC were produced at 14 °C and 16 °C after 74 and 55 h, respectively. The results of this survey indicate that milk used for raw milk cheese production in Ireland poses a limited risk to public health, although further studies on occurrence of toxin producing S. aureus should be undertaken.
KeywordsStaphylococcus aureusRaw milkEnterotoxinsSE genesSEC production
生乳及由其生产的干酪中可能存在产毒素的金黄色葡萄球菌。为了检测在爱尔兰用于生产干酪制品的生乳中产毒素菌的金黄色葡萄球菌的类型和数量,从爱尔兰南部地区5个原料奶的供应商和4个生乳干酪生产厂家收集了117个生乳及其相关产品,采用贝尔德派克兔血浆纤维蛋白原选择性琼脂平板计数法(ISO 688-2)法测定了凝血酶阳性葡萄球,结果表明,样品中凝血酶阳性葡萄球菌菌数在欧盟法规规定的范围之内。采用反向被动乳胶凝集试验(SET-RPLA)测定了金黄色葡萄球菌(从81个阳性样本中分离出的151株菌)产生的肠毒素型SEA-SED,以及应用多重聚合酶链反应(PCR)对sea、seb、sec、sed和see基因进行扩增,实验结果表明83.2%的金黄色葡萄球菌株不含有产肠毒素(SE)的基因或者经检测不具有产肠毒素的能力。仅从1个原料乳供应商所提供的原料乳中分离出的26株金黄色葡萄球菌中检测到了sec基因和具有产肠毒素C的能力,而且这26株分离菌株属于2个不同PEGE基因型。一株产SEC的金黄色葡萄球菌在10%的无菌还原脱脂乳培养基中分别在10 °C和12 °C下培养96和74 h时后,没有肠毒素产生;而在14 °C和16 °C下培养74和55h后,产生了低浓度的SEC。调查结果表明,尽管爱尔兰用于生产干酪的生乳对公众健康影响的风险较低,但仍有必要进一步研究产肠毒素的金黄色葡萄球菌对食品安全带来的潜在危害。