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

Probiotics have been widely adopted due to their beneficial health properties. Here, we investigated the interactions of a probiotic <i>Limosilactobacillus (Lactobacillus) reuteri</i> M4-100, with a translocating <i>Escherichia coli</i> 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 <i>L. reuteri</i> M4-100 in co- and pre-inoculation experiments, its adhesion to the co-culture of cells was significantly reduced (<i>p</i> < 0.0001). A significant reduction in the invasion of the HMLN-1 strain was also observed upon the inoculation of <i>L. reuteri</i> M4-100 with the co-culture 60 min prior to HMLN-1 exposure (<i>p</i> < 0.0001). The <i>L. reuteri</i> M4-100 strain also significantly (<i>p</i> < 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 <i>L. reuteri</i> M4-100 to reduce or inhibit the interaction of <i>E. coli</i> 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.