A Synbiotic of Bifidobacterium animalis subsp. lactis BB-12 and 2′-FL Alleviate Infant Diarrhea and Anxiety-like Behaviors via Gut Microbiota Modulation in an EPEC O127 Infection Model

<b>Background/Objectives</b>: Infant diarrhea is a major global cause of morbidity and mortality. While <i>Bifidobacterium</i> is linked to diarrhea, its preventive effects, underlying mechanisms, and potential synergistic benefits with prebiotics remain unclear. The objective of this study was to explore the efficacy of a synbiotic composed of <i>Bifidobacterium animalis</i> subsp. <i>lactis</i> BB-12 (BB-12) and 2'-fucosyllactose (2'-FL) in alleviating infant diarrhea. <b>Methods</b>: One-week-old C57BL/6J mice were used to construct a model of infant diarrhea via infection with enteropathogenic <i>Escherichia coli</i> (EPEC) O127. Mice were administered BB-12 (10⁸ CFU per mouse), 2'-FL (1 g/kg), or their combination (synbiotic) for three consecutive weeks. <b>Results</b>: Administration of the synbiotic not only markedly improved diarrhea, anxiety-like behavior, colon inflammation, and gut barrier function but also positively reshaped the microbial community. This was achieved through a significant rise in short-chain fatty acid (SCFA)-producing bacteria (e.g., <i>Akkermansia</i> and <i>Paraprevotella</i>), a rise in fecal SCFAs, and a reduction in harmful bacteria such as <i>Escherichia</i>. <b>Conclusions</b>: The synbiotic effectively relieves EPEC-induced infant diarrhea by regulating gut microbiota composition and metabolic functions. These findings highlight its potential as a dietary intervention in infant diarrhea and provide new insights into infant health applications.