Question

Colibactin is a DNA-damaging compound and when taken up by human intestinal cells, colibactin result in double stranded DNA break and can cause human colorectal cancers. It is synthesized by:

• A. Certain strain of E. coli
• B. Helicobacter pylori
• C. Bacteroides fragilis
• D. Bifidobacterium spp.

Hint:

Remember the link: \textbf{Coli}bactin is produced by E. \textbf{coli}. The name of the toxin itself points to its bacterial origin.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question requires identifying the bacterial source of colibactin, a DNA-damaging toxin produced by specific gut bacteria implicated in colorectal cancer development.
Step 2: Detailed Explanation:


Colibactin, a secondary metabolite, is produced by the polyketide synthase (pks) island, a specific genomic region.

This pks island is present in certain strains of Escherichia coli, especially those in the B2 phylogroup, as well as some Klebsiella pneumoniae and other Enterobacteriaceae strains.

These colibactin-producing (pks\(^+\)) E. coli strains are part of the normal gut microbiota in some individuals.

Colibactin can alkylate DNA, causing double-strand breaks in intestinal epithelial cells, potentially leading to chromosomal instability and promoting colorectal cancer.

Helicobacter pylori is linked to stomach cancer, Bacteroides fragilis produces Bacteroides fragilis toxin (BFT) associated with colon cancer, and Bifidobacterium are generally beneficial probiotic bacteria.

Step 3: Final Answer:
Specific E. coli strains synthesize colibactin.