Danger in the nose: multidrug-resistant squatters

One in every three humans carries the bacterium Staphylococcus aureus in their nose. This is no reason to be alert: “Generally, S. aureus just sits there in the nose and doesn’t do anything,” says infection biology expert Simon Heilbronner, Professor of Microbiology at the LMU Biocenter since April 2023. He has even found the germ in his own nose. As so-called opportunistic pathogens, the cocci only cause problems when they get a suitable opportunity, such as entering the bloodstream through open wounds.

But when that happens, S. aureus is extremely dangerous. The pathogen is very good at evading the human immune system, destroying white blood cells, and helping itself to the nutrients in our cells. Ultimately, this leads to systemic infection, which, if left untreated, can culminate in septic shock and, in the worst case, death. When an infection occurs, highly effective antibiotics are the only thing that help – albeit only if you are lucky. S. aureus is one of the notorious hospital bugs, against which drugs are becoming increasingly ineffective. “Worldwide colonization and infection by so-called MRSA strains of the bacterium are continuously rising. These strains are completely resistant against our best antibiotics,” says Heilbronner.

Antibiotic resistance

In Germany, the problem is still more or less under control: around 7 to 10 percent of infections with S. aureus in hospitals are MRSA cases. In the United States, the proportion is much higher at around 50 percent. “The Covid-19 pandemic was a powerful illustration of what happens when untreatable diseases meet a health system that is not prepared for them,” says the biologist. In the case of antibiotic resistance, the threat is not unexpected: “Science is preaching for 30 years that we mustn’t allow this situation to escalate any further. But unfortunately, it’s just like climate change – efforts are not sufficient and we’re walking with open eyes into the abyss.”

This is partly because there is too little money invested in developing new antibiotics. Companies would need to put millions of R&D dollars into the development of a new antibiotic, which would then languish in warehouses because it is only permitted to be used in an emergency as a reserve antibiotic. Ideally, the state would create incentives for companies to continue researching such drugs by means of targeted funding. Moreover, experts are calling on doctors to use antibiotics with greater circumspection and precision so that new resistances do not arise.

The right microbiome

This is where Heilbronner’s research comes into play. He seeks to understand why S. aureus occurs in some noses and not others. To this end, his team is taking a particularly close look at the other inhabitants of the olfactory organ. Observations have shown that certain types of bacteria help or hinder the growth of dangerous pathogens. “If we manage to promote a nasal microbiome that is hostile to S. aureus, we could reduce the demand for antibiotics by preventing infections from happening in the first place,” explains Heilbronner.

Another approach is the development of new diagnostic techniques. With modern analytical methods, we could assess a patients’ individual risk of infection in the future. Heilbronner calls this proactive diagnostics. “If a patient is found to carry highly invasive antibiotic-resistant germs, then doctors would not perform invasive procedures in the first instance, but sanitize the nose before the patient is admitted to hospital.” Through the use of nasal probiotics, for example, it could be possible one day to influence the nasal microbiome to prevent S. aureus colonization and a patient that enters hospital without dangerous pathogens in their nose cannot get infected.

Since his basic courses at university, Heilbronner has been fascinated by the interaction between bacteria and their host. While completing his master’s thesis at the University of Tübingen and his subsequent doctorate at Trinity College Dublin, he was already studying various staphylococci. After he obtained his PhD, he returned to Tübingen as a postdoc, where he later founded a junior research group and established his own research field. He is now further pursuing his research as a professor at LMU: “It’s great to work in a field that is so important for science as well as for the entire society.”