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 asks to identify the bacterial source of colibactin, a genotoxin (a toxin that damages DNA) produced by certain gut bacteria and linked to colorectal cancer.
Step 2: Detailed Explanation:


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

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

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

The colibactin they produce can act as a DNA alkylating agent, causing double-strand breaks in host intestinal epithelial cells. This DNA damage can lead to chromosomal instability and promote the development of colorectal cancer.

Helicobacter pylori is associated with stomach cancer, Bacteroides fragilis can produce a different toxin (BFT) linked to colon cancer, and Bifidobacterium are generally considered probiotic.

Step 3: Final Answer:
Colibactin is synthesized by certain strains of E. coli.