The human gut is home to hundreds of different bacterial species collectively known as the gut microbiome. A major health benefit these provide is to protect the gut against invading pathogens (disease-causing microorganisms) that could cause harmful infections. But up to now, how this protective effect comes about has been unclear, and whether certain bacterial species have a more important role than others.
To investigate this, researchers at Departments of Biology and Biochemistry, tested 100 different gut bacteria strains individually and in combination for their ability to limit the growth of two harmful bacterial pathogens: Klebsiella pneumoniae and Salmonella enterica. Individual gut bacteria showed a very poor ability to restrict the spread of either pathogen. But when communities of up to 50 species were cultured together, the pathogens grew up to 1000 times less effectively than when cultured with any individual species. This ‘community protection effect’ was seen regardless of whether the bacteria were cultured together in vials, or in ‘germ-free’ mice (which had no resident gut bacteria at the start of the experiments).