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 Gut Microbiota

Human individuals can harbor over 150 different microbial species in their gut, which collectively encode more than 100-fold more non-redundant genes than there are in the human genome.[16,24] More recent data, however, has challenged this number, suggesting that the ratio between bacteria and human cells is closer to 1:1.[25] In healthy humans, the intestinal microbiota consists of members of all three domains of life: bacteria, archaea and eukarya, of which the bacterial community is the most abundant and diverse.[8] Nine different bacterial phyla have been recorded in humans so far, of which the bacteroidetes and firmicutes dominate.[8,16,24] Many of these bacteria in the gut have not been cultivated. Recent breakthroughs in the successful culture of the previously 'unculturable' human microbiota have revealed a whole spectrum of novel bacterial species and taxa.[26] The application of novel sequencing techniques provides an opportunity to understand this complex ecosystem much better.[8,13]

The intestinal microbiota plays a critical role in priming the host's immune system, gut maturation and gut functions, such as nutrient uptake and metabolism, mucosal barrier function, enteric nervous system and motility.[27–29] Numerous host genes seem to be specifically altered in response to various members of the microbiota, showing the importance of the microbial composition to the body's response.[30,31]