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How Pneumonia Spreads From the Lungs

Scientists Discover Key Player in Infection

The bacteria that causes pneumonia can spread from the lungs to the bloodstream and present a serious and dangerous complication to the otherwise treatable infection. Until recently, how bacteria moved from the lungs to the bloodstream was unknown. But new research from Alan Hauser, MD, PhD, professor in Microbiology-Immunology and Medicine-Infectious Diseases at Northwestern Medicine, has identified the role of a toxin in this process.

Dr. Hauser and his team of scientists used a mouse model of pseudomonas aeruginosa (PA) pneumonia to study how the pneumonia bacterium introduces a toxin called ExoS to the surrounding cells in the lungs. Notably, the team was able to identify the cells infected with ExoS using a novel imaging technique from the Center for Advanced Microscopy.

Thanks to the use of this leading-edge technology, the Northwestern Medicine scientists made some interesting discoveries about the behavior of the bacterium and toxin. First, they learned that in addition to white blood cells, the bacterium was infecting epithelial cells — the cells that form a barrier between the lung and bloodstream.

Second, the scientists discovered that the bacterium was not randomly infecting epithelial cells. Rather, the scientists were able to show the toxin appeared in specific areas, which they named “fields of cell injection.” Over time, these fields grew larger, and the cells within them began to die. This in turn was associated with the breakdown of the barrier to bloodstream, which allowed the bacteria to spread outside the lungs.

The scientists concluded that the presence of ExoS in cells disrupts the barrier between pulmonary and vascular systems, allowing the bacteria to escape the lungs and travel to the bloodstream.

Implications and Inhibitors

Dr. Hauser believes these findings will form the foundation for future studies to explore the mechanisms in more detail. Specifically, he plans to explore how the ExoS toxin creates the fields of cell injection, which ultimately lead to the barrier breakdown.

Research surrounding the spread of toxins in PA pneumonia may also have implications for different strains of bacteria that can cause pneumonia. Furthermore, with more detail, Dr. Hauser believes scientists could be able to design inhibitors to protect patients with pneumonia in their lungs by preventing bacteria from reaching the bloodstream.