A Feline Milk-Drived Pediococcus acidilactici M22 Alleviates Escherichia coli O157:H7 Infection Through Anti-Adhesion, Anti-Inflammation, and Microbiota Modulation

<i>Escherichia coli</i> O157:H7 is a pathogenic bacterium that causes severe intestinal infections characterized by inflammation and disruption of the intestinal barrier. Probiotic lactic acid bacteria (LAB) from milk can support intestinal health and combat enteric pathogens; however, the potential of feline milk-derived LAB against <i>E. coli</i> O157:H7 infection remains unclear. In this study, <i>Pediococcus acidilactici</i> (<i>P. acidilactici</i>) M22, isolated from feline milk, was evaluated for probiotic activity in vitro and in vivo in a C57BL/6 mouse model of <i>Escherichia coli</i> O157:H7 infection. In vitro assays demonstrated that M22 significantly inhibited the adhesion of <i>Escherichia coli</i> O157:H7 to intestinal epithelial cells. For in vivo assessment, C57BL/6 mice were orally administered M22 prior to infection with <i>E. coli</i> O157:H7. Protective effects were evaluated by monitoring body weight loss, colon length, disease activity index (DAI), myeloperoxidase (MPO) activity, cytokine levels, tight junction protein expression, oxidative stress markers, and gut microbiota composition. M22-treated mice exhibited significantly less body weight loss and lower DAI scores than infected controls. M22 also prevented colon shortening, indicating reduced colonic damage. Probiotic treatment attenuated neutrophil infiltration and mucosal inflammation, as evidenced by decreased colonic MPO activity, reduced levels of pro-inflammatory cytokines, and elevated anti-inflammatory IL-10. Additionally, M22 preserved intestinal barrier function by upregulating tight junction proteins and mitigating infection-induced histopathological changes. M22 supplementation enhanced antioxidant defenses in colonic tissue (lower malondialdehyde, higher superoxide dismutase and glutathione), indicating reduced oxidative stress. Furthermore, gut microbiota analysis (16S rRNA sequencing) revealed that M22 counteracted infection-induced dysbiosis, restoring microbial diversity and a healthy composition (enrichment of beneficial commensals and suppression of harmful bacteria). By safeguarding intestinal integrity and homeostasis, M22 emerges as a promising next-generation probiotic for improving intestinal health in companion animals.