The goal of this observational study is to assess the efficacy and safety of the probiotic Escherichia coli Nissle 1917 (EcN®, Ca.Di.Group S.p.A) in the treatment of symptomatic patients after an episode of both complicated and uncomplicated acute colonic diverticulitis.

The main question it aims to answer are:

• Is the studied probiotic able to significantly reduce symptoms, assessed by means of a validated and dedicated score?
• Is there any difference in microbiota among the study group at baseline and a selected cohort of patients subdivided in subjects with diverticulosis and asymptomatic subjects after an episode of acute uncomplicated diverticulitis or an episode of complicated diverticulitis submitted to surgery with colonic resection without stoma?
• Is there any difference in microbiota in the study group at baseline and after 3 and 6 months of treatment with the probiotic?
• Is there any correlation between microbiota modification and symptoms during follow-up?
• Is there any impact on fecal calprotectin values before and during probiotic therapy?
• Is there any modification of evacuation before and during follow-up?
• Is probiotic able to prevent recurrent episodes of acute diverticulitis during follow-up?
• The safety of the probiotic will be assessed during the follow-up. The study group will be assessed at baseline and during follow-up with a dedicated clinical score and Bristol stool scale. Microbiota and fecal calprotectin values will be also assessed at baseline and during follow-up. Microbiota at baseline will be also evaluated for comparison in the three selected groups with diverticulosis and both asymptomatic and symptomatic after an episode of acute diverticulitis.

Inclusion Criteria:

• Symptomatic patients three months after an episode of uncomplicated acute colonic diverticulitis;
• Symptomatic patients six months after an episode of complicated acute colonic diverticulitis; submitted to .surgical colonic resection without stoma;
• Patients with diverticulosis;
• Asymptomatic patients three months after an episode of uncomplicated acute colonic diverticulitis;
• Asymptomatic patients six months after an episode of complicated acute colonic diverticulitis; submitted to surgical colonic resection without stoma.

Exclusion Criteria:

• Ongoing acute diverticulitis at radiologic assessment
• Antibiotic therapy, both systemic and topic, and/or probiotics and/or mesalazine within four weeks before enrolment;
• Lactulose-lactitol use within four weeks before enrolment;
• Presence of chronic inflammatory bowel diseases;
• Presence of Segmental Colitis Associated with Diverticulitis (SCAD);
• Presence of ischemic colitis;
• Severe chronic liver (Child-Pugh C) and/or pancreatic and/or renal diseases;
• Patients with severe renal failure;
• Presence of suspected/actual pregnancy;
• Presence of recent/ongoing neoplasia, under oncological treatment within 6 months before enrolment;
• Presence of COVID-19 infection;
• Patients unable to give informed consent.

The study population will include the above specified study groups.