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.

Inclusion Criteria:

• Circular stapled anastomosis
• Planned surgery with colo-colic anastomosis
• No passage disorder, as it is confirmed at the first medical examination
• Not allergic to antibiotics
• Can receive a bowel preparation
• No proximal excluded intestine, i.e., the bowel preparation may be successful (ileostomy)

Exclusion Criteria:

• treated with antibiotics within 2 weeks before randomisation
• allergic to any of the medicines used
• under 18 years of age
• have suffered from abdominal sepsis within 6 months prior to recruitment
• pregnancy or breastfeeding
• been treated with steroids
• any form of chronic immunosuppression

All patients undergoing planned colorectal surgery, whether open or laparoscopic, with circular suture anastomosis training are eligible for the study.