SURGIcal COmplication and MIcrobiome ChangeS in Colorectal Surgery

Overview

The microbiome, the collection of microorganisms that live in our gut, plays an important role in maintaining our health, proper nutrient absorption, nutrient turnover and immunity. After birth, a symbiotic relationship develops with the strains of bacteria that colonise our gut, and the presence and proportion of bacteria is individualised and highly variable. A healthy bacterial flora is essential for the cells of the intestinal mucosa. Glycoproteins in the cell surface mucus coat are important nutrients for bacteria, while some bacterial strains supply mucosal cells with nutrient molecules (e.g. short-chain fatty acids) that are their essential energy source. An abnormal change in the proportion of bacterial strains that make up the microbiome, dysbacteriosis, in which pathogenic bacteria proliferate at the expense of members of the normal flora, can cause a number of pathologies. Nutrient supply to the cells of the mucosa is reduced, making them more vulnerable and leading to various pathological conditions. The microbiome and the essential nutrients they produce have also been found to play an important role in wound healing. A decrease in the diversity of the microbiome, an increase in the relative number of pathogenic bacteria and a decrease in the proportion of 'beneficial' bacteria increases the risk of surgical complications of infection and suture failure.

A number of risk factors have been identified that increase or decrease the risk of anastomotic leak. The risk of anastomotic failure is increased by anastomosis (lower third) close to the anus, tumour size greater than 5cm in colorectal carcinoma, surgical complications, smoking, diabetes, male gender, overweight, malnutrition (protein deficiency), heart disease requiring anticoagulation, time to surgery, American Society of Anaesthesiologist score, neoadjuvant treatment, corticosteroid use. The risk of suture failure is reduced by mechanical lining, intravenous and oral non-absorbable antibiotics. The microbiome also appears to have an impact on suture failure: lower diversity of bacteria in intraoperative specimens and an increase in the number of mucin-degrading Bacteroidaceae or Lachnospiraceae strains may be associated with higher anastomotic failure.