27.36 : Bacterial Flora of the Large Intestine

The gut microbiome is formed by a vast and diverse community of bacteria that colonizes our large intestine. These bacteria start residing in the gut from birth and continue diversifying throughout life, influenced by factors such as diet, lifestyle, and stress. The gut bacterial community also includes bacteria from food and those that enter the colon through the anus.

The normal gut flora of the colon plays a critical role in generating essential vitamins such as vitamins K, B5, and B7. Additionally, fermentation makes gut bacteria break down indigestible carbohydrates in foods like beans into short-chain fatty acids. This gas produced during the fermentation is expelled as flatus, a mixture of H₂S, H₂, N₂ (nitrogen), CH₄, and CO₂ gases.

Bacterial enzymes also play a crucial role in breaking down peptide remnants, which generate ammonium ions with indole and skatole—nitrogenous compounds responsible for fecal odor and H2S. Furthermore, the bacteria convert bilirubin to urobilinogens and stercobilnogens for excretion. Stercobilin ultimately gives feces its brown color.

Lastly, harmful bacteria proliferation is effectively controlled by suppression due to the outnumbering of beneficial gut bacteria.