Changes in the lung microbiome may help predict how well critically ill patients will respond to care.
Specifically, patients with higher levels of lung bacteria one day after admission to the ICU Intensive Care Unit ) had fewer ventilator-free days, a strong effect that was not explained by severity of critical illness or the presence of pneumonia.
The identity of lung microbiota was also predictive of ICU outcomes in these patients. Two bacteria normally found in the gut ( Lachnospiraceae and Enterobacteriaceae spp ) were common in the lung microbiome of patients who had worse ICU outcomes.
The presence of Enterobacteriaceae spp in the lung microbiome was also associated with acute respiratory distress syndrome, or ARDS, a life-threatening illness in which the lungs are severely inflamed.
Prior studies found that the immune function of patients with ARDS is highly variable and that the translocation of gut bacteria to the lungs may play a role in the development of ARDS.
In another earlier study, the researchers showed that the lung microbiome in patients with idiopathic pulmonary fibrosis, or IPF, is also predictive of clinical outcomes.
The human microbiome comprises the genetic material of an estimated 100 trillion microbes. Bacteria is the biggest component of the microbiome, but it also includes viruses, fungi and archaea.
Unlike the human genome, which is relatively static, the microbiome is altered, sometimes dramatically, by diet, disease and other factors.
While the lungs have historically been considered sterile, in the past decade investigators have used DNA-based methods to reveal that the lung contain diverse and dynamic communities of bacteria.
In their study of 91 critically ill patients, the researchers controlled for disease severity and for whether the patient had pneumonia, which would increase the number of bacteria in the lung microbiome.
After taking these factors into account, the associations between ventilator-free days and the bacteria level and detection of gut-associated bacteria in the lung microbiome persisted.
The lung microbiome may represent a novel target for preventing and treating critical illness.
Study limitations include the fact that researchers could not control for medications, including antibiotics, that the patients may have taken before being admitted to the ICU.
The researchers could not determine if the gut-associated bacteria found in some patients' lung microbiome had migrated from the lower gastrointestinal tract or whether they were found in the lungs because of aspiration, the accidental inhalation of food or liquid. ( Xagena )
Source: Journal of Respiratory and Critical Care Medicine, 2020