The Emerging Role of the Microbiota in the ICU

Nora Suzanne Wolff; Floor Hugenholtz; Willem Joost Wiersinga


Crit Care. 2018;22(78) 

In This Article

The Link Between the Microbiota and the Gut-lung Axis

The intestinal microbiota has emerged as a key component of both local and systemic immunity. Epithelial and immune cells gain information directly from bacteria and local cytokine responses and subsequently adjust inflammatory responses. Microbiome research combining the gut and lung has started to show an association between the composition of the intestinal microbiota and lung health.[45,46] Experimental germ-free and antibiotic murine models have shown that the body's microbiota is important in the defense against influenza and several types of bacterial pneumonia.[46] Moreover, probiotics containing Lactobacillus spp. and Bifidobacterium spp. have been shown to improve incidence and outcome of respiratory infections. Additionally, exposure to Toll-like receptor (TLR) agonists and nucleotide-binding oligomerization domain (NOD)-like receptors in the intestine, by substances such as lipopolysaccharide (LPS), peptidoglycan and lipoteichoic acid, has been shown to increase the lungs' ability to clear bacteria.[45] These studies suggest that the intestinal microbiota is important for airway defenses. Moreover, human and murine studies have shown that the lungs can contain gut-associated bacteria during sepsis and ARDS. However, this gut-lung axis does not seem to be a one-way street. Pulmonary infection with tuberculosis, influenza and Burkholderia pseudomallei have all been shown to have a significant effect on the composition of the gut microbiome in murine models.[40,47,48] Figure 3 shows a schematic overview of the potential consequences of microbial dysbiosis in the critically ill in both the lung and intestine.

Figure 3.

The gut and lung microbiota in critical illness. A healthy gut microbiome plays a protective role in host defense against local and pulmonary pathogen invasion. In the critically ill, there is often dysbiosis in the lung and intestinal microbiotas, which can contribute to diseases like pneumonia and acute respiratory distress syndrome (ARDS)