Study Finds Neighboring Nasal Bacteria Can Help or Hinder Staphylococcus aureus

Many species of bacteria live together in the human nose, and Staphylococcus aureus is sometimes among them. Although this bacterium can cause serious infections, many people carry it without being aware of it. Scientists still only partly understand why S. aureus persistently colonizes some people but not others.

Research from Ludwig Maximilians University suggests that the bacteria living alongside S. aureus are part of the answer. In a study led by Simon Heilbronner, the team found that these microbial neighbors can either suppress the pathogen or support its growth. Their findings were recently published in Microbiome. 

Whether the neighbors help or hinder depends on several factors, including which nutrients the bacterial community uses up or releases and what the particular S. aureus strain can do metabolically. Because of this, the effects differed widely from one combination of bacterial community and S. aureus strain to another.

“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,” said Heilbronner.

The amino acid tyrosine offered an especially clear example. The nose is a nutrient-poor environment, and the researchers found S. aureus strains there that rely on getting tyrosine from outside sources. Some bacterial communities can fill this gap by supplying tyrosine. Among 512 human S. aureus strains the team tested, 40 grew better when extra tyrosine was added.

Unexpectedly, this dependence can work in the pathogen’s favor. When tyrosine is plentiful, S. aureus can stop making the amino acid itself and save resources. Experiments in mice also showed that these kinds of metabolic differences can affect colonization when other nasal bacteria are present.

The results could help shape future efforts to change the nasal microbiome and push out S. aureus. “If we want to use probiotic bacteria to target S. aureus one day, we first need to understand these interactions,” added Heilbronner. “Our aim is to create communities that deprive the pathogen of the resources it needs—rather than inadvertently supplying it with nutrients.”