Lactobacillus johnsonii DY2 Isolated from Yaks Alleviated Acute Escherichia coli Infection via Modulating Inflammatory Responses, Antioxidant Capacity, and Gut Microbiota

The escalating challenge of antimicrobial resistance has spurred interest in probiotics as alternatives for combating bacterial infections. This study aimed to isolate and characterize probiotic <i>Lactobacillus johnsonii</i> (<i>L. johnsonii</i>) from yak feces with protective efficacy against acute <i>Escherichia coli</i> (<i>E. coli</i>) infection. In vitro, DY2 supernatant inhibited the growth of <i>E. coli.</i> In vivo, mice pretreated orally with DY2 (1 × 10⁹ CFU/mL) for 21 days before <i>E. coli</i> challenge exhibited significantly reduced weight loss (<i>p</i> < 0.001), lower bacterial translocation in the intestines (<i>p</i> < 0.001), and normalized organ indices (<i>p</i> < 0.05) compared to untreated infected controls. DY2 modulated host immune and oxidative responses by significantly lowering serum levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6; <i>p</i> < 0.001 to <i>p</i> < 0.05) and malondialdehyde (MDA; <i>p</i> < 0.001), while elevating levels of the anti-inflammatory IL-10 (<i>p</i> < 0.05) and antioxidant enzymes (SOD, GSH-Px, T-AOC; <i>p</i> < 0.001 to <i>p</i> < 0.01). Histologically, DY2 preserved intestinal mucosal integrity, with reduced villus shortening and inflammatory infiltration (<i>p</i> < 0.001 for villus length in key segments). 16S rRNA sequencing of intestinal microbiota revealed enhanced α-diversity (<i>p</i> < 0.05 to <i>p</i> < 0.001), community stability, and enrichment of beneficial genera such as <i>Butyricimonas</i> in DY2-treated mice. Conclusively, <i>Lactobacillus johnsonii</i> DY2 protects against acute <i>E. coli</i> infection via anti-inflammatory, antioxidant, gut barrier strengthening, and microbiota-modulating activities. Yak-derived lactobacilli are promising probiotics with excellent antibacterial properties.