# Limosilactobacillus reuteri M4-100 Mitigates the Pathogenicity of Escherichia coli Strain HMLN-1 in an Intestinal Epithelial Model and Modulates Host Cell Gene Expression

## TL;DR

This study shows that the probiotic L. reuteri M4-100 can reduce the harmful effects of a translocating E. coli strain in an intestinal model.

## Contribution

The study demonstrates the prophylactic potential of L. reuteri M4-100 against E. coli HMLN-1 through reduced adhesion, invasion, and translocation.

## Key findings

- L. reuteri M4-100 significantly reduced E. coli HMLN-1 adhesion to intestinal cells.
- Pre-inoculation with L. reuteri M4-100 led to a stronger reduction in E. coli invasion and translocation.
- The probiotic modulated host cell gene expression in response to bacterial interactions.

## Abstract

Probiotics have been widely adopted due to their beneficial health properties. Here, we investigated the interactions of a probiotic Limosilactobacillus (Lactobacillus) reuteri M4-100, with a translocating Escherichia coli strain HMLN-1, in a co-culture of cells, representing the intestinal epithelium, and identified molecular mechanisms associated with the host response. A co-culture of Caco-2:HT29-MTX cells was exposed to the HMLN-1 strain and the route of translocation was studied. Scanning and transmission electron microscopy revealed the adhesion of the strain to the microvilli, the establishment of close contact with the co-culture prior to being taken up by membrane-bound vesicles, and translocation via the intracellular pathway. When the HMLN-1 strain was challenged with L. reuteri M4-100 in co- and pre-inoculation experiments, its adhesion to the co-culture of cells was significantly reduced (p < 0.0001). A significant reduction in the invasion of the HMLN-1 strain was also observed upon the inoculation of L. reuteri M4-100 with the co-culture 60 min prior to HMLN-1 exposure (p < 0.0001). The L. reuteri M4-100 strain also significantly (p < 0.0001) reduced the translocation of the HMLN-1 strain in both co- and pre-inoculation experiments. Differential gene expression studies identified key cellular responses to the interaction with these bacteria, both alone. These data demonstrate the efficacy of L. reuteri M4-100 to reduce or inhibit the interaction of E. coli HMLN-1 with the intestinal epithelium. A prophylactic role of this probiotic strain is postulated as these effects were more pronounced in pre-inoculation experiments.