Aged Anti-Bacterial Agents--therapeutic use Cefoxitin--therapeutic use Clindamycin--therapeutic use Clinical Trials as Topic Colectomy Colonic Diseases--surgery Drug Therapy, Combination Female Gentamicins--therapeutic use Humans Intestinal Fistula--etiology Male Middle Aged Postoperative Complications--etiology Preoperative Care Prospective Studies Random Allocation Surgical Wound Infection--prevention & control