Elucidation of Bifidobacterium isolates from human milk and feces: investigating their anti-inflammatory effects on raw 264.7 via NF-κB signaling pathway

This study aimed to identify potent strains from seven Bifidobacterium isolates by evaluating their ability to counteract inflammation triggered by Staphylococcus aureus-derived extracellular vesicles (SA-EVs). Characteristics such as tolerance to simulated gastric and intestinal juice, adhesion/competitive adhesion, antimicrobial activity, and anti-inflammatory effects were investigated. Generation time of tested isolates ranged from 112.27 to 135.24 min, except for Bifidobacterium adolescentis AC19 (64.56 min) and Bifidobacterium longum AC18 (208.20 min). Seven strains, except B. longum CICC6186, remained viable at pH 3.0 (maximal reduction from 10⁸ to 10⁷ CFU/mL), yet were unable to withstand 3.0 g/L bile salts for 3 h (reduced from 10⁸ to 0 CFU/mL). They demonstrated good competitive adhesion ability against Staphylococcus aureus and Escherichia coli on Caco-2 cells with an average of 55.86% and 57.41% reduction of bacteria/cell, respectively, and showed strong antimicrobial ability against both Gram-positive and Gram-negative bacteria, possibly via production of acid and bacteriocins. Heat-inactivated Bifidobacterium (10⁶ CFU/mL) inhibited the inflammation triggered by SA-EVs, most likely by suppressing RAW-BLUE™ proliferation into M1 and TNF-α secretion, in turn affecting the activation of the NF-κB signaling pathway. B. longum AC15 showed overall outstanding capabilities amongst all, especially the adhesion ability to enterocytes, tolerance to acid and bile salt, and anti-inflammatory ability on macrophages.