Staphylococcus aureus is carried harmlessly in the noses of many people, yet it can turn into a dangerous pathogen when it breaches the body's defences. A team led by Simon Heilbronner, Professor of Microbiology at LMU's Biocenter, has now shown that whether the bacterium can establish itself in the nasal cavity depends heavily on the other microbes already in residence, and on the nutrients those neighbours consume or release.
Writing in the journal Microbiome, the researchers describe the amino acid tyrosine as a telling example. In the nutrient-poor environment of the nose, some S. aureus strains rely on an external supply of tyrosine, which certain bacterial communities can provide. Of 512 human S. aureus strains tested, 40 grew more strongly when extra tyrosine was available, and strains with a plentiful supply could stop producing the amino acid themselves, saving precious resources.
Experiments in mice confirmed that these metabolic differences influence colonisation when other nasal bacteria are present. The outcome, the team argues, is that the nasal microbiome cannot be neatly sorted into protective and harmful species: the same neighbour can help or hinder a pathogen depending on strain and context. Understanding these exchanges is a prerequisite for probiotic strategies designed to assemble communities that deprive S. aureus of what it needs.