This study will compare the types of bacteria in the colon before and after colon resection surgery. The investigator will also compare standard post-operative antibiotic treatment to flagyl (metronidazole) treatment post-operatively to see if giving the antibiotic, decreases the incidence of return of Crohn's disease.

Participants who are scheduled for colon resection for Crohn's disease will be invited to take part in this randomized study. Participants will be randomized 1:1 to either Metronidazole 250 mg three times a day, starting after surgery, for three months, or the local usual standard of care after surgery, which may be a different antibiotic prescribed by the physician.

Participants will also provide a stool sample at the following time points: prior to surgery, the day of discharge, at their follow-up appointment (usually about two weeks after surgery), three months, and six months.

Participants will also be followed to determine their clinical outcome.

Inclusion Criteria:

• 20-80 years old who is deemed an acceptable surgical candidate for ileocolic resection.

Exclusion Criteria:

• any patients that are dependent on total parenteral nutrition and unable to tolerate oral intake
• patients who will undergo resection but will have an ileostomy created
• patients on maintenance antibiotics for their disease