Lung bacteria could help to predict clinical outcomes in critically ill patients

Researchers have found that lung bacteria could help to predict how well people in intensive care will respond to treatment.

• Gut-lung connection
• Therapy targets

What is already known on this topic
Recent studies have revealed that the lung microbiota of critically ill patients is altered. But little is known about whether differences in lung bacteria help to explain who recovers and who doesn’t.

What this research adds
By studying more than 90 critically ill patients, researchers found that the composition of the lung microbiota predicted how well people responded to care. Two types of bacteria normally found in the gut—Lachnospiraceae and Enterobacteriaceae—were common in the lung microbiota of patients who had worse outcomes, measured as ventilator-free days.

Conclusion
The lung microbiota could be a new therapeutic target for the prevention and treatment of life-threatening respiratory conditions, the researchers say.

Changes in the composition of the lung microbiota have been associated with several lung conditions. Now researchers have found that lung bacteria could help to predict how well people in intensive care will respond to treatment.

The study, published in the American Journal of Respiratory and Critical Care Medicine, could have important implications for the treatment of patients in intensive care. Knowing that the gut microbiota differs among people with life-threatening respiratory conditions may help clinicians to change patients’ outcomes for the better, says study senior author Lieuwe Bos, a researcher in pulmonology and critical care at the University of Amsterdam. “We can’t change our patients’ genes or their chronic diseases, but we can potentially change their bodies’ microbiota,” he says.

Recent studies have revealed that the lung microbiota of critically ill patients is disrupted, and this disruption is associated with altered lung immunity. But little is known about whether differences in lung bacteria help to explain who recovers and who doesn’t.

To find out if the clinical outcomes of critically ill patients are predicted by features of the lung microbiota, Bos and his colleagues studied 91 people within 24 hours of admission to the intensive care unit (ICU) of a university hospital. First, the team looked at the patients’ lung microbes; then, the researchers analyzed how many days each patient could go without a ventilator—a medical device that provides oxygen to people who are unable to breathe on their own.

Gut-lung connection

Nearly a month after being admitted to ICU, people with higher levels of lung bacteria at the time of admission had fewer ventilator-free days than people with lower levels of lung bacteria.

Rather than the severity of the patients’ illness or the presence of pneumonia, it was the lung microbiota composition that was predictive of ICU outcomes, measured as ventilator-free days. Two types of bacteria normally found in the gut—Lachnospiraceae and Enterobacteriaceae—were common in the lung microbiota of patients who had worse outcomes.

The presence of Enterobacteriaceae in the lung microbiota was also associated with acute respiratory distress syndrome, a life-threatening condition that occurs when fluid builds up in the lungs.

Therapy targets

The findings suggest that the lung microbiota could be a new therapeutic target for the prevention and treatment of life-threatening respiratory conditions, the researchers say. But the team cautions that they couldn’t determine if the bacteria found in people’s lungs had migrated from the digestive tract or whether the patients had accidentally inhaled food or liquid containing the microbes.

“What the current study tells us is that this disruption of lung microbiota is clinically meaningful,” says study lead author Robert Dickson, a microbiologist and immunologist at the University of Michigan.

The researchers note that the next step will be determining whether altering lung bacteria influences patients’ outcomes. “Predicting ICU outcomes is important, but what we really want is a target for therapy,” Dickson says. “We need to figure out if the lung microbiome is something we can modify, either to prevent lung injury or to help it resolve faster,” he says.