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

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