Could the effects of air pollution be mediated by the mix of bugs in our airways? It seems that exposure to pollutants correlates with differences in the species of bacteria living in our respiratory tracts. This may be a hidden link between pollution and disease.

Numerous studies have shown that air pollution raises our risk of certain conditions, such as heart disease and stroke. Even in the UK, which has relatively clean air, pollution is blamed for up to 50,000 premature deaths a year.

Why this link exists, however, is unclear. To look into one possible cause, Jacopo Mariani and his colleagues at the University of Milan, Italy, took nasal swabs from 40 people living in and around Milan to investigate whether pollution affected the types of bacteria that colonise our airways.


Just like the gut, our airways contain a community of microbes, most of which are harmless. In fact, some probably offer us benefits. The team used genetic sequencing to identify the bacteria present, and compared these types with levels of air pollution recorded by nearby monitoring stations.

Higher levels of particulates in the air from three days before sampling correlated with a lower diversity of bacteria in the nasal swabs. This could be a bad thing, says Mariani, because decreased diversity might affect the functions that bacteria provide to the host.

For instance, the concentration of Actinobacteria, the dominant group in a healthy microbiome, was lower in volunteers exposed to higher levels of pollution. The part that these bacteria play in the body is not yet clear, but they are known to produce compounds with antimicrobial and anti-inflammatory properties.

Another group of bacteria that can cause harmful respiratory infections, Moraxella, was typically found in greater concentrations in people exposed to higher pollution levels.

Not to be sniffed at

This study is the first to look at how air pollution levels relate to types of respiratory microbe in healthy people, says Mariani, who presented the work this week at the European Respiratory Society International Congress in Milan. “We want to assess how this modification could impact on human health status and how it could be responsible for respiratory disease,” he says.

Analysing changes in bacteria in the airways might give us an early indicator of problems before disease develops, he adds.

Lidwien Smit at Utrecht University in the Netherlands says this is an area that deserves more attention. “You’re inhaling stuff that might cause inflammatory responses in your airways, so it’s extremely likely that the airway microbiome is a sort of mediator between pollution and respiratory effects… but this area of research is still in its infancy.”

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