Bifidobacteria, one of the predominant species which live in the gut, form a barrier against infection, shows research in Gut. But only certain strains are effective. The belief that certain gut bacteria can be beneficial is longstanding, but controversial.
Fourteen strains of bifidobacterium, taken from infant stool samples, were cultured and tested against a wide range of harmful bacteria, including those associated with gut infections.
Two strains, CA1 and F9, decreased the numbers of bacteria, prevented them entering other cells, and killed off a strain of salmonella. The two strains also colonised the intestinal tract of mice, protecting them against lethal infection with salmonella.
How the bifidobacteria develop their "antibiotic" substances is not known, but they are thought to work in concert with the antibiotic proteins and enzymes released by specialised cells in the gut lining, so producing a barrier against infection.
Bifidobacteria are found in breast milk and can be increased by eating more fibre rich foods and "live" yoghurt.