# Lacticaseibacillus rhamnosus D1 Fermented Milk Confers Protection Against Typhoid Fever Through Immunomodulation and Gut Microbiota Regulation in Mice

## TL;DR

Fermented milk with Lacticaseibacillus rhamnosus D1 protects mice from typhoid fever by boosting immunity and balancing gut bacteria.

## Contribution

Demonstrates that L. rhamnosus D1 fermented milk protects against typhoid via immunomodulation and microbiota regulation in mice.

## Key findings

- Fermented milk improved survival, reduced bacterial translocation, and lessened weight loss in infected mice.
- L. rhamnosus D1 suppressed pro-inflammatory cytokines and upregulated anti-inflammatory and antimicrobial peptides.
- Fermented milk altered gut microbiota, promoting beneficial microbial lineages like Muribaculum and Roseburia.

## Abstract

This study investigated the protective effect of fermented milk by Lacticaseibacillus rhamnosus D1 in a murine model of Typhoid fever, focusing on cytokines, antimicrobial peptides and microbiota modulation. BALB/c mice were pre-treated with milk fermented by L. rhamnosus D1 prior to Salmonella Typhimurium challenge. Outcomes assessed included survival, weight change, bacterial translocation, mRNA expression of cytokines and antimicrobial peptides, in addition to gut microbiota modulation. Mice receiving fermented milk exhibited higher survival rates, reduced bacterial translocation and attenuated weight loss compared to controls. mRNA expression analyses revealed that L. rhamnosus D1 pre-treatment suppressed the expression of pro-inflammatory cytokines (IFN-γ, IL-6 and IL-12) and upregulated anti-inflammatory cytokines (IL-5, IL-10 and TGF-β), as well as antimicrobial peptides (Reg3β, Reg3γ and Lcn2). Furthermore, we observed that the consumption of fermented milk changed the gut microbiota of infected mice, not only by modulating the existing taxa, but also by facilitating the emergence of unique, potentially beneficial microbial lineages, such as Muribaculum, Roseburia, Intestinimonas, Bdellovibrio and Facklamia. These findings indicate that L. rhamnosus D1 protected mice against S. Typhimurium infection through immunomodulatory and microbiota-mediated mechanisms, changing mucosal immunity and strengthening the intestinal barrier by modulating gut microbiota and immune responses, in addition to promoting host antimicrobial defenses.