Gut Competition Dynamics of Live Bacterial Therapeutics Are Shaped by Microbiome Complexity, Diet, and Therapeutic Transgenes

Competitive exclusion is conventionally believed to prevent the establishment of a secondary strain of the same bacterial species in the gut microbiome, raising concerns for the deployment of live bacterial therapeutics (LBTs), especially if the bacterial chassis is a strain native to the gut. In this study, we investigated factors influencing competition dynamics in the murine gut using isogenic native Escherichia coli strains. We found that competition outcomes are context-dependent, modulated by microbiome complexity, LBT transgene expression, intestinal inflammation, and host diet. Furthermore, we demonstrated that native LBTs can establish long-term engraftment in the gut alongside a parental strain, with transgene-associated fitness effects influencing competition. We identified various interventions, including strategic dosing and dietary modulation, that significantly enhanced LBT colonization levels by 2 to 3 orders of magnitude. These insights provide a framework for optimizing LBT engraftment and efficacy, supporting their potential translation for human therapeutic applications.