牛至精油对腐生葡萄球菌抑制作用机制

Action Mechanism of Oregano Essential Oil against Staphylococcus saprophyticus

为研究牛至精油对腐生葡萄球菌(Staphylococcus saprophyticus)的作用机制,本实验采用琼脂平板打孔法,通过抑菌圈直径确定牛至精油对腐生葡萄球菌的最小抑菌浓度(minimum inhibitory concentration,MIC),由微生物生长曲线、电导率、碱性磷酸酶(alkaline phosphatase,AKP)活性、乳酸脱氢酶(lactate dehydrogenase,LDH)活性、紫外物质吸收与扫描电子显微镜(scanning electron microscopy,SEM)观察来综合评价牛至精油对腐生葡萄球菌的作用效果。结果:牛至精油对腐生葡萄球菌的MIC为0.25%,菌体经MIC与2 MIC牛至精油处理后,其进入对数生长期的时间明显延滞,菌体内容物大量外泄,胞外AKP与LDH活力明显提高,菌体生长受到影响,其作用效果与处理的体积分数呈正相关。同时,菌体细胞壁与细胞膜的结构发生改变,扫描电子显微镜观察结果表明腐生葡萄球菌经MIC牛至精油处理6 h后,菌体发生变形;而经2 MIC牛至精油处理后,其表面破裂、外膜剥落,最终导致菌体死亡。因此,牛至精油通过破坏腐生葡萄球菌菌体细胞壁与细胞膜的完整性来发挥其抑菌作用。

The action mechanism of oregano essential oil(OEO) against Staphylococcus saprophyticus was investigated in this paper. The minimum inhibitory concentration(MIC) was determined by measuring inhibition zone diameter using the agar well diffusion method, and bacterial growth curve, electrical conductivity, alkaline phosphatase(AKP) activity, lactate dehydrogenase(LDH) activity, ultraviolet absorption and scanning electron microscopy(SEM) were used to evaluate the antimicrobial effect of OEO. The results showed that the MIC of OEO against Staphylococcus saprophyticus was 0.25%. When treated by OEO at MIC or 2 MIC, the logarithmic phase was delayed obviously, accompanied by the leakage of intracellular contents and increased significantly activities of AKP and LDH. The bacterial growth was concentrationdependently inhibited by OEO, with structural changes of the cell wall and membrane being observed. The SEM results revealed that the bacterial cells appeared morphologically deformed after being treated with OEO at MIC for 6 h, and OEO at 2 MIC caused cell surface disruption, outer membrane detachment and finally cell death. Our findings support that OEO exerts its bacteriostatic effect by destroying the integrity of the cell wall and membrane.