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

## TL;DR

A probiotic bacteria from yak feces, Lactobacillus johnsonii DY2, helps protect against E. coli infection by reducing inflammation, boosting antioxidants, and improving gut health.

## Contribution

Lactobacillus johnsonii DY2 from yaks is shown to protect against E. coli infection through multiple mechanisms, including gut microbiota modulation.

## Key findings

- DY2 reduced weight loss, bacterial spread, and organ damage in mice infected with E. coli.
- DY2 lowered inflammation and oxidative stress while boosting antioxidant enzymes in infected mice.
- DY2 improved gut microbiota diversity and enriched beneficial bacteria like Butyricimonas.

## Abstract

This study explored a beneficial bacterium, Lactobacillus johnsonii DY2, isolated from the feces of yaks, to see whether it could help protect against acute Escherichia coli infection. The increasing problem of antibiotic resistance makes it necessary to find safe, natural alternatives to prevent and control bacterial diseases. Laboratory tests showed that DY2 can inhibit E. coli growth. When given to mice for three weeks before infection, DY2 reduced disease severity—preventing weight loss, lowering bacterial spread, and maintaining normal organ health. It also reduced inflammation and oxidative stress by balancing key immune molecules and boosting antioxidant enzymes. Under the microscope, DY2-treated mice showed healthier intestinal tissues compared to infected controls. Moreover, gut microbial analysis revealed that DY2 increased the diversity and abundance of beneficial bacteria, helping restore gut balance during infection. These findings suggest that Lactobacillus johnsonii DY2 enhances natural defense systems through anti-inflammatory, antioxidant, and microbiota-stabilizing effects. This yak-derived probiotic could be a promising and environmentally friendly tool to help protect animals and humans from infections in an era when antibiotic resistance is a growing concern.

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 Lactobacillus johnsonii (L. johnsonii) from yak feces with protective efficacy against acute Escherichia coli (E. coli) infection. In vitro, DY2 supernatant inhibited the growth of E. coli. In vivo, mice pretreated orally with DY2 (1 × 109 CFU/mL) for 21 days before E. coli challenge exhibited significantly reduced weight loss (p < 0.001), lower bacterial translocation in the intestines (p < 0.001), and normalized organ indices (p < 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; p < 0.001 to p < 0.05) and malondialdehyde (MDA; p < 0.001), while elevating levels of the anti-inflammatory IL-10 (p < 0.05) and antioxidant enzymes (SOD, GSH-Px, T-AOC; p < 0.001 to p < 0.01). Histologically, DY2 preserved intestinal mucosal integrity, with reduced villus shortening and inflammatory infiltration (p < 0.001 for villus length in key segments). 16S rRNA sequencing of intestinal microbiota revealed enhanced α-diversity (p < 0.05 to p < 0.001), community stability, and enrichment of beneficial genera such as Butyricimonas in DY2-treated mice. Conclusively, Lactobacillus johnsonii DY2 protects against acute E. coli infection via anti-inflammatory, antioxidant, gut barrier strengthening, and microbiota-modulating activities. Yak-derived lactobacilli are promising probiotics with excellent antibacterial properties.