A Genomically Safe Lactobacillus johnsonii Lacking Mobile Antimicrobial Resistance Genes Suppresses Escherichia coli and Modulates Gut Microbiota and Diarrhea Incidence in Suckling Piglets.

Enterotoxigenic Escherichia coli (ETEC) causes significant mortality and economic losses in piglet production. This study aimed to identify a safe, effective probiotic for E. coli control under practical conditions. Using a green fluorescent protein-tagged ETEC screening platform, we identified three Lactobacillus johnsonii (LJ) strains with potent antimicrobial activity. LJ FBU1718 demonstrated superior efficacy against multidrug-resistant ETEC, high gastrointestinal tolerance, and strong mucin adhesion. In IPEC-J2 cells, LJ FBU1718 reduced ETEC-induced inflammation, preserved epithelial integrity, and decreased cytotoxicity. Whole-genome sequencing confirmed its safety, showing an absence of mobile antimicrobial resistance elements. In suckling piglets, LJ FBU1718 supplementation improved growth and survival while enhancing fecal consistency. These benefits were underpinned by gut microbiota modulation, where Lactobacillus enrichment and E. coli reduction correlated with a significant decrease in diarrheal incidence. These findings establish LJ FBU1718 as a safe, practical probiotic candidate to enhance productivity in swine production.