Microbiota of the Large Intestine

The large intestine hosts the highest microbial density in the human body.

Most microbes here are anaerobic bacteria, predominantly from the phyla Bacillota and Bacteroidota, with Pseudomonadota present at lower levels.

The cecum contains facultative anaerobes, such as Escherichia and Enterococcus, as well as aerotolerant bacteria like Lactobacillus.

The proximal colon is rich in strict anaerobes, including Bacteroides and Clostridium. These microbes are highly active in fermenting dietary fibers into short-chain fatty acids.

The distal colon harbors strict anaerobes such as Ruminococcus and Faecalibacterium.

These bacteria continue to ferment the remaining dietary fibers. They are also the key producers of butyrate, which nourishes colon cells.

The large intestine also hosts methanogenic archaea, such as Methanobrevibacter smithii. These archaea consume excess hydrogen produced during fermentation and convert it into methane.

Fungi like Candida are present in low abundance and participate in carbohydrate metabolism, but their contribution is minor compared to bacteria.