Chronic alcohol consumption causes an imbalance in the bacterial communities living in the gastrointestinal tract (referred to as the gut microbiome). Alcohol abusers are particularly susceptible to lung infections with Klebsiella pneumoniae bacteria, which can sometimes cause severe pneumonia and death. Using a mouse model of infection, researchers from the Louisiana State University Health Sciences Center demonstrated that alterations in the gut microbiome from chronic alcohol consumption increases susceptibility to K. pneumoniae infection in the lungs.
These studies were initiated by feeding one group of mice with the chronic alcohol diet, while a control group received a normal diet. Feces were collected from these mice and transplanted into a second set of mice (orally, but hey, mice do that anyway!) that had previously been treated with antibiotics to eliminate the normal microbial flora in the gut. In this way, the researchers were able to completely replace the normal mouse gut microbiome with abnormal microbiomes from mice that had consumed alcohol (or control mice that had normal diet). This approach allowed the researchers to directly measure the contribution of the microbiome in recipient animals, without worrying about direct effects of alcohol consumption.
Next, both groups of mice were infected with K. pneumoniae. Mice with an imbalanced-microbiome had more severe infection then those with a healthy microbiome. Mice with an imbalanced microbiome had less immune cells known as T-lymphocytes in their lungs, whereas increased numbers of T-lymphocytes were found in the gastrointestinal tract. This suggests that the impaired defense against the K. pneumoniae infection was due to a sequestering of T-cells in the gastrointestinal tract. Mice with an imbalanced microbiome also had increased inflammation in the lungs and evidence of intestinal barrier damage, which leads to chronic inflammation, and a higher susceptibility to K. pneumoniae.
The mortality of alcoholic patients hospitalized with pneumonia is known to be around 64 percent, whereas in non-alcoholics the mortality rate is approximately 20 percent. This new research is the first to demonstrate how imbalances in gut bacteria can lower immune defences against lung infections. This study is also an important reminder of how human organ systems are interconnected, and the importance of helpful microbes in maintaining human health. This is an important advancement in the battle against pneumonia, which causes approximately 423,000 people to visit the emergency room every year, and 50,622 deaths every year.
Summary written by: Serena Drouillard
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Alcohol-associated intestinal symbiosis impairs pulmonary host defence against Klebsiella pneumonia
