More of the Gut in the Lung: How Two Microbiomes Meet in ARDS

Abstract

In critically ill patients, lung and gut microbiomes undergo profound changes. Lung microbiome might become enriched with gut-associated microbes as recently demonstrated in sepsis and acute respiratory distress syndrome (ARDS). It has been proposed that in these conditions, bacteria from the gut might enter the lungs via translocation, a process facilitated by increased gut and alveolo-capillary permeability. In patients requiring mechanical ventilation after severe trauma, lung microbiome enrichment with gut-associated microbes was found to correlate with the development of ARDS. The lungs in ARDS are increasingly susceptible to opportunistic infections which can further perpetuate alveolar inflammation and injury. Undoubtedly, more research on the gut-lung crosstalk in critically ill patients is needed to identify causal relationships between the altered microbiome, infections, inflammation, and acute lung injury. With further insights, this area of investigation could lead to the development of novel, microbiome-targeted, and immunomodulation strategies with the potential to improve outcomes of critically ill patients with sepsis, trauma, and ARDS.

Keywords: ARDS; bacterial translocation; critically ill; microbiome; nosocomial infection; sepsis.

Figure 1

Pulmonary microbiome in health and critical illness. In healthy individuals, lungs and gut harbor markedly different microbiomes. Composition of lung microbiome closely resembles the one of oropharynx. In critically ill patients with sepsis, severe trauma, or ARDS, lung microbiome might become enriched with gut-associated microbes. Potential pathogens can enter lung via aspiration and possibly translocation from the gut. The resulting state of dysbiosis promotes inflammation and acute lung injury.