Bifidobacterium spp.

A key genus for the gut barrier, B-vitamin synthesis and immune modulation. Bifidobacterium falls sharply with age and with antibiotic use.

What bifidobacteria do in the gut

Bifidobacteria specialise in short-chain sugars: in infants in the oligosaccharides of breast milk, later in inulin, fructo-oligosaccharides and breakdown products of starch. Through their own metabolic pathway, the bifid shunt, they ferment these into acetate and lactate without producing gas. The acids lower the pH in the gut, make it harder for pathogens to settle and serve other bacteria as raw material for butyrate. Some strains produce folate and other B vitamins. Bifidobacteria influence the immune system of the mucosa, for example the formation of protective IgA and regulatory T cells.

Low bifidobacteria – what happens in the gut?

With few bifidobacteria, less acetate and lactate are produced: the pH in the large intestine rises, pathogens and protein-fermenting microbes find space more easily, and butyrate producers receive less starting material. Short-chain sugars are then fermented to a greater extent by gas-producing bacteria. The amount typically falls after antibiotics and with increasing age; studies have also observed low levels more often in irritable bowel and in childhood allergies.

High bifidobacteria – what happens in the gut?

High amounts usually arise when many short-chain sugars reach the large intestine. The vigorous acid production lowers the pH markedly. If few bacteria are present that further process lactate, lactate can accumulate and bind water in the gut, which makes the stool softer. Bifidobacteria in the small rather than the large intestine are unusual and are looked at in questions about small intestinal colonisation.

The interpretation is given in your report.