Gut Microbiome in the Critically Ill

Each organ and system of the human body has its own specific microbial composition. The intestinal microbiome has many functions: production of short-chain fatty acids, which are necessary substrates for enterocyte function; defense against infections of the digestive tract; bidirectional communication between the gut other organs. Intensive care unit (ICU) dysbiosis is a loss of health-promoting commensal microbes and an increase in pathogenic microbes. Nowadays, two ICU-enterotypes have been identified: ICU-enterotype I, which comprises predominantly Bacteroides and an unclassified genus of Enterobacteriaceae, and ICU-enterotype II, which comprises predominantly Enterococcus. Among strategies aimed at improving the outcome in critically ill patients, the use of antibiotics could be reduced as they do not only kill pathogens but also “health-promoting” microbes. Additionally, oral/enteral nutrition should be preferred over parenteral nutrition. Fecal microbiota transplantation should also be considered for restoring healthy gut microbiota, although little literature is available in the ICU setting.