Bacterial Flora of the Large Intestine

The vast and varied community of bacteria colonizing the large intestine forms the gut microbiome.

Bacteria start residing in the gut at birth and diversify throughout life, influenced by diet, lifestyle, and stress.

The gut bacterial community includes bacteria from ingested food and those entering the colon via the anus.

The normal gut flora of the colon generates crucial vitamins, including vitamins K, B₅, and B₇.

Besides synthesis, gut bacteria break down indigestible carbohydrates in certain foods, like beans, into short-chain fatty acids through fermentation.

This fermentation produces small amounts of flatus — a mixture of H₂S, H₂, N₂, CH₄, and CO₂ gases.

These bacteria also convert bilirubin to urobilinogens and stercobilinogens, which eventually form pigments that are excreted in feces, giving it a yellow-brown color.

Bacterial enzymes break down peptide remnants, generating ammonium ions with indole and skatole—nitrogenous compounds responsible for the fecal odor and H₂S.

Lastly, the proliferation of harmful bacteria is effectively controlled by being outnumbered by beneficial gut bacteria.