Mechanical bowel preparation for left-sided colorectal surgery remains standard in most cases. However, there are some discrepancies on how to prepare the bowl, while rectal enema and oral agents are both available methods.

The knowledge of intestinal microbiome role on surgical outcomes is increasing, since few recent reports linked microbiome composition to postoperative complications, such as anastomotic insufficiency. Although, it is not clear how the bowel preparation affects the gut microbiome. Therefore, different bowel preparation techniques impact on gut microbiome will be studied.

Inclusion Criteria:

1. Age ≥ 18 y.;
2. Signed informed consent;
3. Left-side colorectal resection for colorectal cancer;

Exclusion Criteria:

1. Anticipated ileostoma;
2. Allergy to oral preparation agents;
3. Multivisceral surgery;
4. Emergency surgery;
5. History of inflammatory bowel disease;
6. History of surgery disrupting gastrointestinal tract integrity;
7. Signs of tumor obturating the lumen of the bowel;
8. Pregnancy;