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CF Patients Increase Bacterial Load But Lose Bacterial Diversity As They Age, Study Finds

Cystic fibrosis (CF) patients have more bacteria but lower bacterial diversity in their lungs than people without CF — yet bacterial diversity diminishs with age in CF patients, a large multicenter study found.

CF is characterized by recurrent airway infection, inflammation and progressive decline in lung function. Genetic mutations in these patients induce a salt imbalance, leading to airway surface dehydration and the buildup of thick and sticky mucus. This creates an ideal habitat for bacteria, which is why chronic bacterial lung infections are the leading cause of death in CF.

The airways of CF patients usually harbor complex bacterial communities, also referred to as microbiota. Yet not much is known about the variability of these airway communities and their dynamics during disease.

For this reason, researchers at Ann & Robert H. Lurie Children’s Hospital of Chicago — through the Stanley Manne Children’s Research Institute — aimed to characterize the microbiota in the lungs of CF patients and determine its relationship to inflammation and disease status. To do that, they analyzed lung fluid samples from 136 pediatric CF, 10 adult CF and 45 pediatric disease control participants for total bacterial load and for microbiota diversity.

Among CF patients, scientists found that airway microbiota differed substantially by patient’s age. Children younger than 2 years old with CF had a higher diversity of bacteria than did children 6 years or older, with a lower proportion of classical CF pathogens (namely Pseudomonas, Staphylococcus and Stenotrophomonas).

With increasing age and increasing inflammation, microbiota diversity decreased, with traditional CF-associated bacteria comprising more than 70 percent of the airway communities from older CF patients.

“As diverse microbiota communities were most common in the youngest patients, determining the clinical impact of these bacteria and factors contributing to the development of traditional CF flora may improve early treatment,” the team wrote.

Scientists also found that non-classical CF pathogens were dominant in 20 percent of both pediatric and adult CF patients. The clinical impact of non-traditional pathogens in CF is still unclear.

CF patients displayed higher bacterial loads, lower diversity and distinct community structures than did non-CF pediatric controls. The team believes that exposure to traditional CF pathogens may be common in CF and non-CF patients, but the host environment or exposure to antibiotics may alter the survival of these microbes within the community.

“We use a lot of antibiotics to treat CF lung disease, which can reduce the number and diversity of normal bacteria in the lung. We do not know whether this decreased bacterial diversity contributes to lung disease in cystic fibrosis or is just a side effect of treatment,” Dr. Susanna McColley, the study’s co-author, said in a press release.

“To address this question we could study the effects of giving antibiotics over time, or examine if there are ways to manipulate the bacterial diversity in the lungs with probiotics,” she added. “Our study results could have important impact on generating hypotheses and designing intervention studies to improve outcomes for patients with cystic fibrosis.”

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