People don't generally consider the lungs as an important component of the human microbiome. Of course, our lungs are not sterile and have their own diverse bacteria with functions and influence that are still under investigation. Unfortunately, lung bacteria can also cause an inflammatory response, which can be especially harmful after lung transplant as it can lead to pneumonia and bronchiolitis obliterans syndrome (BOS) - both of which can lead to death.
A recent study published in PLoS ONE by researchers at the University of Michigan investigated the bacterial population and diversity of bacteria in 33 people undergoing lung transplants. They discovered that after lung transplant the bacterial diversity of the lung microbiome decreases. Furthermore, based on controls with non-transplant populations, that low diversity of lung microbiome is associated with higher risk for infection. Finally, they discovered that one particular bacteria, Pseudomonas aeruginosa, was associated with BOS. This is especially interesting because Pseudomonas fluorescens, a different species of Pseudomonas, was not associated with BOS, meaning clinical sampling of bacterial families and genera are not valuable in diagnosing risk of BOS.
Like any major surgery, transplant patients receive antibiotics to fight infection. Perhaps with this evidence that lung microbiome diversity is important to lung health, lung probiotics should be considered after transplantation.