Whether Staphylococcus aureus can establish itself in our noses also depends on the bacteria living alongside it. LMU researchers have shown that these microbial neighbors can either promote or inhibit the pathogen.

Our noses are home to many different species of bacteria living side by side. One of them may be S. aureus. Many people carry this bacterium without knowing it, although it can cause serious infections. Why S. aureus colonizes some people persistently but not others remains only partly understood.

How the nasal microbiome can help drug-resistant bacteria thrive

A new study led by Simon Heilbronner, Professor of Microbiology at LMU's Biocenter, shows that other members of the nasal microbiome play an important role. They can not only inhibit S. aureus but also encourage its growth. Key factors include which nutrients the community consumes or releases and the metabolic capabilities of the particular S. aureus strain. As a result, the effects varied considerably depending on the bacterial community and S. aureus strain involved. The team recently published its findings in the journal Microbiome.

“Our findings show that we cannot simply divide the nasal microbiome into ‘good’ and ‘bad’ bacteria. What matters is which microorganisms live together and which nutrients they make available to one another or compete for,” says LMU biologist Simon Heilbronner.

This was particularly clear in the case of the amino acid tyrosine. The researchers identified S. aureus strains that depend on an external supply of tyrosine in the nutrient-poor environment of the nose. Certain bacterial communities can make up for this shortage by making tyrosine available. When the team tested 512 human S. aureus strains, additional tyrosine boosted growth in 40 of them.

Can we reshape the microbiome?

Surprisingly, this dependence can even be beneficial: When enough tyrosine is available, S. aureus can conserve resources by no longer producing the amino acid itself. Experiments in mice also showed that such metabolic differences can influence colonization in the presence of other nasal bacteria.

The findings could also inform future strategies to reshape the nasal microbiome and displace S. aureus. “If we want to use probiotic bacteria to target S. aureus one day, we first need to understand these interactions,” says Heilbronner. “Our aim is to create communities that deprive the pathogen of the resources it needs – rather than inadvertently supplying it with nutrients.”