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 Potential Clinical Relevance of the Gut Microbiota on the ICU

An imbalance in the homeostasis or 'dysbiosis' of the gut microbiota has been associated with a range of different diseases, including diabetes, obesity, inflammatory bowel disease and rheumatoid arthritis.[5,6] This association with disease has led to investigations into the gut microbiota's involvement at the systemic level. In the critically ill, the intestinal microbiota has been analyzed in a couple of studies so far. In general, we can state that critically ill patients admitted to the ICU have a state of dysbiosis of the intestinal microbiota.[32–34] Figure 2 shows a schematic representation of the composition of the intestinal microbiota in the critically ill in comparison to a healthy human. Overall, the intestinal microbiota of critically ill patients admitted to the ICU with sepsis is characterized by lower diversity, lower abundance of key commensal genera (such as Faecalibacterium, Blautia, Ruminococcus), and in some cases overgrowth (over 50% relative abundance) by one genera, such as Escherichia/Shigella, Salmonella, Enterococcus, C. difficile or Staphylococcus.[32–36]

Figure 2.

Intestinal microbiota in health and critical illness. The microbiota in a healthy individual is a diverse ecosystem with beneficial and commensal bacteria and low abundances of opportunistic pathogens, which are not harmful in small numbers. As a result of certain therapies, such as antibiotics, the microbial composition can be disrupted. The intestinal microbiota of critically ill patients is less diverse and contains more opportunistic pathogens and less beneficial and commensal bacteria

A normal, healthy intestinal microbiota protects against an invasion of pathogens like Enterococcus faecium, Escherichia coli and C. difficile. It comes as no surprise that severe infections caused by these pathogens often occur in patients with a recent history of antibiotic use. The microbiota of these patients is therefore probably disrupted, which allows for the overgrowth of antibiotic-resistant pathogenic and opportunistic bacteria that are frequently encountered in hospital settings.[37]

In sepsis, the focus often lies on the identification of a single pathogen as the causative agent. However, there is an increasing realization that most pathogens do not act in isolation and that infections have 'polymicrobial' phenotypes and are thus linked to the status of the microbiota in the patient. The initial state of the microbiota can influence susceptibility to infection[38] and severity of infection.[39] Recent preclinical data derived from animal models suggest that the gut microbiome plays a protective role in the host defense against sepsis.[39–41] As an example, antibiotic induced disruption of the gut microbiome leads to increased inflammation and bacterial dissemination in murine models of both Gram-positive and Gram-negative pneumosepsis.[39,40] ICU patient data have suggested that the loss of microbiome diversity could predict the length of stay of patients on the ICU further underscoring the potential clinical relevance of the gut microbiome for intensive care medicine.[33]