The composition of bacteria living inside the lungs of people with non-cystic fibrosis bronchiectasis tends to remain stable over time, and may correlate with patients’ lung function, a study says.

The findings of the study, “A longitudinal characterization of the Non-Cystic Fibrosis Bronchiectasis airway microbiome,” were published in the journal Nature Scientific Reports.

Bronchiectasis is a chronic lung disease that causes abnormal thickening of the airways, and excessive production of mucus. The condition may be associated with cystic fibrosis (CF), a serious genetic lung disease. When associated with bacterial infections, it is known as non-cystic fibrosis bronchiectasis, or nCFB.

“Our knowledge of infections in non-cystic fibrosis bronchiectasis (nCFB) lags behind that in CF. Whereas the lung microbiome of pediatric CF patients is dynamic and changes throughout their adolescence, by adulthood a core climax community evolves which remains relatively stable thereafter,” the researchers said.

“However, how the microbiota changes over time and associates with disease progression remains to be elucidated,” they added.

In this longitudinal study, a group of researchers from the University of Calgary in Canada set out to characterize the composition of bacteria living in the lungs of people with nCFB over a long period of time (up to 16 years). One of their main goals was to look for possible relationships between lung bacteria composition and patients’ clinical outcomes.

Researchers gathered a total 133 sputum (mucus expelled by coughing) samples from 29 nCFB patients over the course of 4 to 16 years. Bacterial DNA was isolated and analyzed by genetic sequencing, to determine which species of bacteria were living in the patients’ lungs. Patients’ demographic and clinical data also were recorded.

Surprisingly, the investigators found no significant changes in bacteria composition in nCFB patients over time, suggesting that the lung microbiome (the group of bacteria living inside the lungs) tends to remain stable within each individual.

Genetic analyses revealed that Pseudomonas aeruginosa was present in 45% of the samples, while Haemophilus influenzae was only found in 13%. Interestingly, patients whose samples were positive for P. aeruginosa tended to show higher lung function decline at the study’s start, compared with those whose samples were positive for H. influenzae.

The scientists also found that nCFB patients whose samples contained less bacteria diversity were more likely to experience lung function decline, compared with those whose samples contained higher bacteria diversity.

However, analyses failed to identify a particular species, or a group of bacteria species, that were associated with patients’ lung function decline.

“To our knowledge, this study represents the longest examination of the nCFB microbiome to-date suggesting that the lung microbiome is relatively stable over time, and is highly individualized. We suggest that the lung microbial diversity may be an important contributor to clinical course — although this is likely but one of many host, organism/community and environmental factors,” the researchers said.

“[F]urther studies exploring the microbiome’s association with subsequent clinical outcomes are warranted in our attempt to develop biomarkers for patient prognostication,” they added.