Lactobacillus helveticus mitigates diarrhea and inflammation induced by enterotoxigenic E. coli through rebalance of gut microbiota

The probiotic potential and mechanisms of <i>Lactobacillus helveticus</i> against <i>Escherichia coli</i> (ETEC) induced diarrhea remain poorly understood, despite its robust physiological traits and long history of safe use. Here, we compared the anti-diarrheal efficacy of four <i>L. helveticus</i> strains (H1-H4) isolated from different geographical origins to unravel the mechanisms of action in ETEC-infected mice. Surprisingly, feeding with <i>L. helveticus</i> strains significantly reduced pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ) and interleukin-6 (IL-6), alleviated jejunal damage, and restored the colon length. Among them, <i>L. helveticus</i> H3 exhibited the best protective effects through upregulation of aquaporin 3 (AQP3) and interleukin-10 (IL-10) and downregulation of heat-stable enterotoxin (ST) and toll-like receptor 4 (TLR4). Notably, ETEC infection disrupted intestinal homeostasis of microbiota by enriching <i>Akkermansia</i> and <i>Escherichia-Shigella</i> and suppressing <i>Lactobacillus</i>, <i>Odoribacter</i>, <i>Alistipes</i>, <i>Ligilactobacillus</i>, and <i>Bifidobacterium</i>; whereas the supplementation with <i>L. helveticus</i> could effectively restore the balance of gut microbiota. Moreover, the strain H3 significantly enhanced the production of several short-chain fatty acids (SCFAs), including butyric, propionic, isobutyric, valeric, isovaleric, and caproic acids, compared to the others. Comparative genome analysis revealed that the strain H3 had more genes that likely contributed to SCFA production, toxin detoxification, and colonization capacity, which support its better efficacy in alleviating ETEC-induced diarrhea. Collectively, our study suggests that <i>L. helveticus</i> alleviates ETEC-induced diarrhea by rebalancing gut microbiota and is a promising probiotic for treating infectious diarrhea.