Researchers Narrow In On Common Cystic Fibrosis Infection

Lung infections are common for cystic fibrosis patients. Puwadol Jaturawutthichai/Shutterstock

Cystic fibrosis patients are prone to lung infections that can be deadly. One of the most common infections – caused by Pseudomonas aeruginosa bacteria – is particularly difficult to treat. The opportunistic bacteria is able to persist even after treatment. Researchers from the University of Washington have just discovered why: After the bacterium infects the lungs, populations become isolated and then evolve region-specific traits.

Cystic fibrosis is characterized by the buildup of mucus in the lungs and other organs. This sticky and thick substance is an ideal breeding ground for bacteria. While a combination of different treatments are able to eliminate large swaths of P. aeruginosa, the bacterium is still able to replicate and survive in a patient’s lung. It is able to persist because different populations become isolated from one another, move to different parts of the lung and then evolve.

According to lead researcher Dr. Peter Jorth, bacterial populations found in different parts of the lung “varied dramatically in terms of their antibiotic resistance and virulence."

“This diversity could affect the patients' health,” he said in a statement. While treatment can eliminate one population of P. aerigunosa, another in a different region can live on.

How the opportunistic bacteria P. aeruginosa genetically diversifies during cystic fibrosis infections. Jorth et al./Cell Host & Microbe 2015

For the study, published in the journal Cell Host & Microbe, researchers dissected lung specimens removed from patients with cystic fibrosis during lung transplantations. They discovered that although all the P. aeruginosa found in the lung originated from a single strain, each population in different regions functioned differently. Genetic sequencing revealed that this diversity arose as each population of P. aeruginosa evolved locally to the region they inhabited.
 
“Even when a single strain of bacteria causes a chronic infection, evolution with human organs can produce diverse families of related bacteria,” senior author Dr. Pradeep Singh said in a statement. “This may be part of what makes treatment so difficult, because when bacteria sensitive to one kind of stress are killed, functionally different siblings are there to take their place.”
 
Researchers suggest that these findings could shed some light on other chronic infections, which could have similar diverse populations of bacteria. Their next challenge is to find new ways to attack this diverse array of bacteria and improve treatment for patients. 
 
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