bioRxiv2026
Inflammatory Bowel Disease (IBD) remains an area of major unmet need, and the undefined composition and manufacturing burden of fecal microbiota transplantation have motivated a shift toward single-strain Live Biotherapeutic Products (LBPs). Swarming bacteria are enriched in the stressed gut and limit mucosal damage, but no human-derived swarming strain has been developed as an LBP. We therefore report the complete preclinical development of Enterobacter ludwigii LS57, a swarming strain isolated from human feces. Chemistry, Manufacturing and Controls (CMC) covered a three-tier cell bank, 30 L fed-batch fermentation and a colon-targeted enteric-coated capsule, enabling consistent pilot-scale production. No treatment-related findings emerged in safety pharmacology (Sprague-Dawley rats) or in single-dose and Good Laboratory Practice (GLP)-compliant 1-week repeat-dose toxicity studies (Sprague-Dawley rats and Beagle dogs). LS57 was identified as E. ludwigii by 16S rRNA and whole-genome sequencing and produced metabolites with reported anti-inflammatory activity in culture. In Dextran Sulfate Sodium (DSS)-induced colitis, LS57 reduced weight loss, preserved colon length, lowered colonic pro-inflammatory cytokines and remodeled the gut microbiota. It also attenuated Trinitrobenzene Sulfonic Acid (TNBS)-induced colitis and enhanced the effect of ciclosporin A. In vitro, LS57 was non-hemolytic, non-cytotoxic, and acid-labile, formed no biofilm, and its resistance to aminopenicillins, cephamycins and imipenem was not transferable by conjugation. In vivo, LS57 colonized the inflamed colon without translocation in wild-type and interleukin-10-deficient mice, and experimental bacteremia was treatable with gentamicin or levofloxacin. LS57 combines efficacy across two mechanistically distinct colitis models with a safety package that addresses the principal regulatory concerns for LBPs, and a scalable manufacturing process, compatible with current good manufacturing practice, in which enteric coating overcomes the strain's poor gastric survival. These data support clinical development of LS57 in IBD.