Designer Probiotics for Effective Inflammatory Bowel Disease Therapy
- Designer E.coli Nissle and L. reuteri strains reduce intestinal pathology and inflammatory cytokine production in the DSS-induced murine model of colitis.
- Designer probiotics outcompete the parent probiotic strain under anoxic growth conditions to improve probiotic survival in the gut.
- Designer probiotics express surface adhesion proteins that promote colonization of the gut.
Inflammatory bowel disease (IBD) is a chronic condition and major health burden in Western countries. Probiotic therapy is a potential treatment option for IBD. While several probiotics have undergone clinical testing as potential therapeutic agents for gut health, most clinical trials have reported limited or no efficacy in IBD patients. Probiotics face strong competition when trying to colonize the gut and very few studies have shown long-term colonization. Probiotic attachment to the intestinal epithelium is an important factor in the successful colonization of the gut. Another important factor relates to the highly oxidized environment of the gastrointestinal tract during periods of inflammation. The abundance of reactive oxygen species (ROS) causes alterations to the intestinal microbiome and puts probiotic species at a survival disadvantage due to their low tolerance to ROS. Genetically engineered strains of probiotics designed to target the specific limitations of commonly used probiotics may lead to improved colonization and persistence in the inflamed intestinal environment.
Pathogenic microorganisms have evolved sophisticated strategies to enable colonization and immune evasion within the host environment. Unlike probiotics, pathogenic bacteria have adapted to outcompete the host’s microbiota for an ecological niche using specific molecular mechanisms. The GbpA adhesion protein facilitates gut colonization of Vibrio cholerae and gpbA deletion mutants cannot colonize. Similarly, strains that possess a metabolic advantage can overgrow other microbes in the hostile environment of the inflamed gut. Salmonella enterica Typhimurium produces a tetrathionate reductase enzyme (encoded by the ttr operon) that can use tetrathionate generated by ROS during inflammation as a respiratory electron acceptor, thereby promoting its outgrowth over competing microbes. UBC researchers have developed designer probiotics that exploit these valuable pathogenic traits to improve the clinical effectiveness of commonly used probiotic strains by enhancing their attachment and stress survival capabilities within an oxidized and inflamed IBD gut.
The inventors have developed designer probiotics that express a binding domain from the gbpA gene of V. cholera to enhance the surface attachment and colonization of the probiotic. The integration of the ttr operon from Salmonella enterica into the genome of the probiotic strain results in improved survival in the presence of ROS species. The genetically modified strains showed reduced ulcer development, improved clinical pathology scoring and reduced the inflammatory cytokine response as compared to the parent strain when tested in the mouse DSS colitis model.
Figure 1: Designer E. coli and L. reuteri modified probiotics are more protective than natural probiotics in a model of DSS-induced colitis. (A) Designer DSS-induced colitis groups show reduced histopathological damage scores compared to parent groups, indicating that designer probiotics protected against DSS-colitis more effectively than the natural probiotics. (B) Epithelial integrity, immune cell infiltration, ulceration, and goblet cell depletion were used to calculate histopathological scores.