Abstract: This study systematically investigated the inhibitory activity of Bifidobacterium longum subsp. longum BD3150 and its cell-free supernatant (CFS) against enterohemorrhagic Escherichia coli O157:H7 (EHEC O157) using the co-culture assay and the agar diffusion method. When 2’-fucosyllactose (2’-FL) served as the sole carbon source, the relative abundance of EHEC O157 after 6 and 18 h of co-culture with B. longum subsp. longum BD3150 was 72.3% and 67.8%, respectively, which was lower than that observed using glucose as the sole carbon source. The antibacterial activity of CFS from B. longum subsp. longum BD3150, cultivated in modified de Man-Rogosa-Sharpe (MRS) medium, was further characterized. The optimum culture conditions were found to be an inoculation size of 3.0%, incubation temperature of 37 ℃, and incubation time of 36 h. A negative correlation was observed between the diameter of the inhibition zone and the pH of the CFS. Furthermore, by adjusting the pH of the CFS and performing centrifugal ultrafiltration (3 kDa, 7 500 × g for 25 min), it was revealed that the inhibitory activity against EHEC O157 was attributed to organic acids.

Key words: Bifidobacterium; antibacterial activity; agar diffusion method; cell free supernatant; human milk oligosaccharides

摘要： 采用共培养和琼脂扩散法评价长双歧杆菌长亚种BD3150及其无细胞发酵上清液对肠出血性大肠杆菌 O157:H7（enterohemorrhagic Escherichia coli O157:H7，EHEC O157）生长的抑制作用。结果表明，以2’-岩藻糖基 乳糖作为唯一碳源，共培养6、18 h后EHEC O157相对丰度较以葡萄糖为碳源下降至72.3%和67.8%。进一步研究 菌株长双歧杆菌长亚种BD3150在改良MRS培养基中所得发酵上清液的抑菌特性，确定其最佳制备条件为接种量 3.0%、发酵温度37 ℃、发酵时间36 h，同时发现抑菌圈直径与上清液pH值呈负相关。通过调节无细胞发酵上清液 的pH值和超滤离心（3 kDa、7 500×g、25 min），发现无细胞发酵上清液中主要抑菌物质为有机酸。

关键词: 双歧杆菌；抑菌活性；琼脂扩散法；无细胞上清液；母乳寡糖