Pathogenic Lung Microbes Respond to Body’s Stress Signals

You’ve heard of the microbiome of our gut, but how about the microbiome of the lungs? Researchers at the University of Michigan Medical School have started to study the connection between susceptibility to potentially life-threatening lung infections like pneumonia, and the bacterial species found in our respiratory system.

A new study published in the American Journal of Respiratory and Critical Care has identified a damaging feedback loop which may explain why some people are more at risk of developing lung infections compared to others. The group at the University of Michigan found that the growth of certain strains of bacteria found in the lung was induced in response to “distress signals” released by the body.

Catecholamines, including adrenaline, are released by the body in response to injury or stress. While previous research showed that some bacteria show elevated levels of cell division when exposed to catecholamines, this study was the first to demonstrate a relationship between the stress hormones and changes in the lung’s microbiome.

The researchers studied 40 samples collected from lung transplant patients and found that levels of catecholamines in the lung were strongly associated with the presence of respiratory infection, and the absence of the community of bacteria normally comprising the lung microbiome. Of the bacterial species colonizing the diseased lung, most were commonly identified as strains that were responsive to catecholamines in the lab.

Robert Dickson, M.D., an assistant professor of internal medicine at the University of Michigan says, “Our findings suggest that the human and bacterial cells in our lungs are speaking the same language. Our lung’s immune cells respond to infection by making catecholamines. Our findings suggest that these catecholamines can, in turn, make certain dangerous bacteria grow faster, which cause more inflammation and stress signaling. It’s a vicious cycle.”

While this research provides new information about the microbes found in our lungs, this is a relatively new field of study which is often dwarfed by the plentiful research available on the gut microbiome. Though medical textbooks still assert that the lung only contains bacteria during decease states, Dickson and his colleagues maintain that while it may contain fewer bacteria compared to our digestive tract, the ecosystem present in out lungs is still medically important.

“The lungs have their own anatomy, their own physiology, and their own ecology,” says Dickson. “The rules from the gut microbiome may not apply. We need to start thinking about how pneumonia and other lung diseases emerge from the complex ecosystem of our respiratory tract.”

The researchers have recently published multiple articles on the lung microbiome and its importance in both healthy individuals and those with infections of the lung.

Sources:

• What’s lurking in your lungs? Surprising findings emerge from microbiome research – http://medicalxpress.com/news/2015-08-lurking-lungs-emerge-microbiome.html
• Dickson, R., Erb-Downward, J., Prescott, H., Martinez, F., Curtis, J., Lama, V., and Huffnagle, G. (2015). Intraalveolar catecholamines and the human lung microbiome. Am. J. Resp. Crit. Care. 192(2), 257-259.