Dr. Bryan Coburn is an infectious diseases specialist at UHN and scientist at Toronto General Hospital Research Institute. Dr. Tereza Martinu is a lung transplant respirologist at UHN's Ajmera Transplant Centre and scientist at Toronto General Hospital Research Institute. (Photo: UHN StRIDe Team)

A recent study led by Drs. Tereza Martinu and Bryan Coburn at Toronto General Hospital Research Institute looked at how chronic acid reflux – known as gastroesophageal reflux disease – affects the communities of microbes found in the lung.

The composition of microbial communities in the lung after transplantation differs between people and can be associated with lung dysfunction and inflammation.

"We wondered whether chronic reflux changed the microbial community, or microbiota, in the lung after transplantation," says Dr. Martinu.

To explore the effect of chronic reflux on lung health after transplantation, the research team compared samples of lung microbiota from individuals who received a lung transplant between 2010 and 2015. Of these individuals, 24 of them experienced chronic acid reflux in the first year after transplant and 51 did not.

Analyses of the data revealed that the density and diversity of the microbial community differed in those with chronic reflux, compared to those without reflux. However, those with the condition were not more likely to experience inflammation and dysfunction of the lung.

When the team considered all samples from the 75 individuals that participated in the study, they identified three different types of microbial community profiles: the first type had high bacterial density, with species that are commonly found in the mouth. The second type had low bacterial density. And the third type had varying densities but with species that often cause infectious disease. This third type was more likely to be associated with lung inflammation and dysfunction.

Individuals with chronic acid reflux were more likely to have the first type of profile.

The research team identified bacteria using fluid samples collected from transplanted lungs. Staphylococcus (illustrated above) was one of the disease-causing species of bacteria that was identified in a subset of lungs. (Photo: Getty Images)

"We found that patients with chronic reflux had increased bacterial density with more species that are commonly found in the mouth," says Dr. Martinu, who is also a lung transplant physician at UHN's Ajmera Transplant Centre and associate professor of Medicine at the University of Toronto (U of T). "Despite having higher levels of bacteria, these individuals did not experience more lung dysfunction than those without chronic reflux in general."

"Chronic acid reflux is an important modulator of the microbial community in the lung after transplantation. Future studies of chronic reflux in the context of transplantation should include the microbial community profile as part of the assessment," concludes Dr. Coburn, who is also an assistant professor of Laboratory Medicine & Pathobiology at the U of T.

Rapid tests for lung microbiota may be useful predictors of disease to help lung transplant recipients manage their health in the future.

This work was supported by the Canadian Institutes of Health Research, UHN's Ajmera Transplant Centre, U.S. National Institutes of Health, Comprehensive Research Experience for Medical Students Program, Cystic Fibrosis Foundation and UHN Foundation.

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