More mouth bacteria diversity tied to worse IPF lung function: Study

But 1 species of bacteria was tied to better lung function, lower death risk

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by Steve Bryson, PhD |

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An illustration provides a close-up view of an assortment of bacteria.

Adults with idiopathic pulmonary fibrosis (IPF) who had greater diversity of mouth bacteria tended to have worse lung function and a higher risk of death than did those with a less diverse bacteria population in their mouths, a new large-scale study shows.

Interestingly, however, those with a higher proportion of a species of bacteria called Streptococcus mitis had better lung function and lower death risk, according to the study, “Commensal Oral Microbiota, Disease Severity and Mortality in Fibrotic Lung Disease,” published in the American Journal of Respiratory and Critical Care Medicine.

Several studies have shown that changes in the lung microbiome — the bacteria and other microbes that live in the lungs — are associated with the progression of IPF, a condition marked by scarring, or fibrosis, in the lungs.

These observations prompted the launch of the Phase 3 CleanUp-IPF trial (NCT02759120), which evaluated the impact of two broad-spectrum antibiotics on hospitalization or survival rates in 513 adults with IPF. Data showed that the addition of these antibiotics to standard treatment failed to delay hospitalization or prolong patient survival.

Because mouth bacteria may serve as a source for microbes in the lungs, a team led by scientists at the University of Michigan examined bacteria populations on cheek swabs collected from patients during CleanUp-IPF. Their goal was to understand the role of the oral microbiome in lung disease, according to a university press release.

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Findings contrast with studies tying bacteria diversity to better health

The team used gene sequencing techniques to assess bacteria composition in cheek swab samples taken from 511 CleanUp-IPF participants. Microbiome data were then correlated with measures of IPF severity.

Data showed that a greater diversity of mouth bacteria in IPF patients was significantly associated with a 73% higher risk of death and worse lung function as assessed by forced vital capacity, which indicates the maximum amount of air that can be forcibly exhaled from the lungs after a deep breath.

Increasing [mouth bacterial] diversity predicts disease severity and death in IPF.

The findings contrast with those of several other studies showing that a greater diversity of bacteria in the lungs and gut generally indicates better health.

At the same time, however, the researchers found that a higher proportion of a group of bacteria called Streptococcus, which was mainly comprised of bacteria from a specific species called Streptococcus mitis, significantly correlated with a lower risk of death and better lung function in certain patients who were not treated with antibiotics.

The protective relationship between oral Streptococcus mitis and IPF was not found among CleanUp-IPF participants who had received antibiotics, the researchers found.

Lead author David O’Dwyer, MD, PhD, of the division of pulmonary and critical care medicine at the University of Michigan Medical School, said Streptococcus mitis tends to act as a gatekeeper against other bacterial threats, including those that can cause periodontal (gum) disease.

Overall, the researchers wrote, “increasing buccal microbial diversity predicts disease severity and death in IPF.”

“The oral commensal Streptococcus mitis spp [species] associates with preserved lung function and improved survival,” they added.