Schubert Justyna, Podkowik Magdalena, Bystroń Jarosław, Bania Jacek
Department of Food Hygiene and Consumer Health Protection, Wrocław University of Environmental and Life Sciences, Wrocław, Poland.
Department of Food Hygiene and Consumer Health Protection, Wrocław University of Environmental and Life Sciences, Wrocław, Poland.
Int J Food Microbiol. 2016 Oct 17;235:36-45. doi: 10.1016/j.ijfoodmicro.2016.06.043. Epub 2016 Jul 1.
Twenty Staphylococcus aureus strains harboring seh gene, including one carrying also sec gene and 11 sea gene, were grown in BHI+YE broth and milk and were tested for SEA, SEC and SEH production. All strains decreased pH of BHI+YE broth at 24h and increased them at 48h. Seventeen S. aureus strains grown in milk changed pH for no >0.3 unit until 48h. Three other S. aureus strains significantly decreased pH during growth in milk. All S. aureus produced SEH in BHI+YE broth in amounts ranging from 95 to 1292ng/ml, and from 170 to 4158ng/ml at 24 and 48h, respectively. SEH production in milk by 17 strains did not exceed 23ng/ml at 24h and 36ng/ml at 48h. Three S. aureus strains able to decrease milk pH produced 107-3029ng/ml and 320-4246ng/ml of SEH in milk at 24 and 48h, respectively. These strains were grown in milk and BHI+YE broth with pH stabilized at values near neutral leading to a significant decrease of SEH production. Representative weak SEH producers were grown in milk at reduced pH resulting in moderate increase in SEH production. SEA was produced in milk by 10S. aureus strains at 24-151ng/ml at 24h, and 31-303ng/ml at 48h. SEA production in milk was higher or comparable as in BHI+YE broth in 3 strains and lower for remaining strains. Production of SEC by sec-positive S. aureus strains was lower in milk than in BHI+YE broth, ranging from 131 to 2319ng/ml at 24 and 48h in milk and 296-30,087ng/ml in BHI+YE at 24 and 48h. Both lacE and lacG transcripts involved in lactose metabolism were significantly up-regulated in milk in strong SEH producers. In these strains hld, rot and sarA transcripts were up-regulated in milk as compared to weak SEH producers. Stabilization of milk pH at a value of raw milk significantly down-regulated hld, rot and sarA RNA in strong SEH producers. Milk was generally found unfavorable for enterotoxin production. However, certain S. aureus strains were not restricted in SEH and SEA expression in milk, unlike SEC which remained down-regulated in this environment. Therefore, low safety risk related to S. aureus producing SEC in milk, as suggested previously, may not pertain to certain SEA and SEH-producing strains.
20株携带seh基因的金黄色葡萄球菌菌株，包括1株同时携带sec基因和11株携带sea基因的菌株，在脑心浸液肉汤（BHI）+酵母提取物（YE）肉汤和牛奶中培养，并检测SEA、SEC和SEH的产生情况。所有菌株在24小时时降低了BHI+YE肉汤的pH值，并在48小时时使其升高。17株在牛奶中生长的金黄色葡萄球菌菌株在48小时前pH值变化不超过0.3个单位。另外3株金黄色葡萄球菌菌株在牛奶生长过程中显著降低了pH值。所有金黄色葡萄球菌在BHI+YE肉汤中产生的SEH量在24小时时为95至1292ng/ml，在48小时时为170至4158ng/ml。17株菌株在牛奶中24小时时SEH产量不超过23ng/ml，48小时时不超过36ng/ml。3株能够降低牛奶pH值的金黄色葡萄球菌菌株在牛奶中24小时时产生107 - 3029ng/ml的SEH，48小时时产生320 - 4246ng/ml。这些菌株在pH值稳定在接近中性的牛奶和BHI+YE肉汤中生长，导致SEH产量显著下降。代表性的弱SEH产生菌株在较低pH值的牛奶中生长，导致SEH产量适度增加。10株金黄色葡萄球菌菌株在牛奶中24小时时产生SEA的量为24 - 151ng/ml，48小时时为31 - 303ng/ml。3株菌株在牛奶中的SEA产量高于或与BHI+YE肉汤中的相当，其余菌株较低。sec阳性的金黄色葡萄球菌菌株在牛奶中产生SEC的量低于BHI+YE肉汤，牛奶中24小时和48小时时为131至2319ng/ml，BHI+YE中24小时和48小时时为296 - 30087ng/ml。参与乳糖代谢的lacE和lacG转录本在强SEH产生菌株的牛奶中均显著上调。与弱SEH产生菌株相比，这些菌株中的hld、rot和sarA转录本在牛奶中上调。将牛奶pH值稳定在生牛奶的值显著下调了强SEH产生菌株中的hld、rot和sarA RNA。一般发现牛奶不利于肠毒素的产生。然而，某些金黄色葡萄球菌菌株在牛奶中SEH和SEA的表达不受限制，与SEC在这种环境中仍然下调不同。因此，如先前所述，与牛奶中产生SEC的金黄色葡萄球菌相关的低安全风险可能不适用于某些产生SEA和SEH的菌株。
