Investigating the effects of vitamin D3 and 5-aminosalicylic acid (Mesalazine) on the expression of virulence determinants in Escherichia coli isolated from patients with IBD and colorectal cancer.

Aim: Based on studies, E. coli strains producing colibactin are selectively enriched in patients with IBD and CRC. This finding raises the possibility that the mentioned compounds may affect this organism and prompted us to conduct this study.

Background: Currently, vitamin D3 is highly recommended in the therapeutic management of inflammatory bowel disease (IBD) and colorectal cancer (CRC). Similar to 5-Aminosalicylic acid (5-ASA) which is a mainstay in treatment of IBD and prevention of CRC related inflammation, the importance of vitamin D3 is also mainly attributed to a series of known protective effects of this compound, particularly regulation of immune response and gut microbiota.

Methods: The antimicrobial effects of vitamin D3 and 5-ASA against E. coli isolated from patients with CRC, IBD, and healthy individuals were assessed by microdilution broth. The expression of virulence-associated genes (clbN, ompC, chuA and yfgL) in isolates treated with these compounds was tested by real-time PCR.

Results: Neither vitamin D3 nor 5-ASAinhibited bacterial growth at the investigated concentrations. The expression of clbN and ompC significantly decreased in vitamin D3-treated isolates (p= 0.01, p= 0.02, respectively). This downregulation was also significant in isolates from the CRC group in comparison with those from IBD patients and healthy individuals.

Conclusion: Vitamin D3's effect on downregulating colibactin, one of the proposed factors in colon carcinogenesis, highlights another unknown aspect of this multifaceted drug. The inability of both studied compounds to inhibit the growth of E. coli may show their benefit in not disturbing the balance of the microbiota.