SEARCHING FOR NEW GUT FRIENDS: IN VITRO CHARACTERIZATION OF THE PROBIOTIC PROPERTIES OF HUMAN COLONIC ISOLATED ESCHERICHIA COLI.

Introduction. Inflammatory bowel diseases (IBDs) are chronic inflammatory condition of the gastrointestinal tract (GI), and include ulcerative colitis (UC) and Crohn’s disease (CD) both characterized by an altered mucosa structure, systemic biochemical disorders due to intestinal altered permeability and extended modification of the gut microbial composition. Patients present reduced microbial diversity often in combination with a lower abundance of obligate anaerobic bacteria and an expansion of facultative anaerobic bacteria, particularly from the Proteobacteria phylum. Indeed, stable colonization by Escherichia coli pathotypes (e.g. Adherent Invasive E. coli (AIEC) or E. coli belonging to the B2 phylogroup) is frequently observed in patients suffering from IBDs. Then, the replacement of E. coli pathotypes with commensal strains is considered a valuable approach for the treatment of IBDs. Specific formulations of probiotics were shown to be effective if administrated in conjunction with standard therapies in patients suffering from IBDs and one of the most used probiotic is the E. coli strain Nissle 1917 (EcN). Although EcN possesses all the characteristics to be the ideal probiotic, the results in terms of contributing to/maintaining the remission of inflammatory diseases as well as preventing the relapse of the diseases are extremely variable affecting its efficacious applications. Hence, this project aimed at selecting several heterogeneous E. coli isolates collected from the colonic mucosa of healthy subjects to develop a new probiotic product enriched in commensal strains beneficial for IBD patients. Materials and Methods. From our previously described E. coli collection, genotypically different isolates sharing common phenotypic features were assayed for their probiotic properties including fitness-associated factors, such as (i) metabolic requirements (competitive capability to metabolize simple sugars and dietary proteins in comparison to different E. coli pathotypes), (ii) production of microcins and colicines and (iii) evaluation of competitive planktonic and sessile growth against selected E. coli pathotypes. EcN was used as control. Results. Commensal E. coli isolates can be classified as faster or slower growing depending on the sugar metabolized in comparison to EcN. As EcN, 4 isolates were able to produce and release thermolabile molecules showing inhibitory activity against different E. coli pathotypes. Competitive planktonic and sessile growth indicated the capability of commensal E. coli isolates to restrict E. coli pathotypes growth. Conclusions. Our in vitro characterization demonstrates that intra-species competition represents an efficient strategy to reduce the burden of E. coli pathotypes. This feature could help the development of new E. coli-based probiotic formulations whose efficacy should be tested to improve the quality of life of patients suffering from IBDs.