Influence of bowel preparation and antimicrobials on colonic microflora.

The influence of three types of preoperative mechanical bowel preparation on colonic microflora has been studied in 88 patients undergoing elective bowel resection and compared with 21 controls. Neither conventional bowel preparation (CBP) using oral magnesium sulphate, enemas and rectal washouts nor whole bowel irrigation (WBI) via a nasogastric tube influenced the type or number of organisms in the colon at the time of operation. The administration of an elemental diet (ED) was associated with only a small reduction the numbers of Escherichia coli (P less than 0.02). The addition of oral neomycin and metronidazole for 48 h before operation to all three methods of bowel preparation was associated with a highly significant reduction in the counts per ml of E. coli (P less than 0.001) and Bacteroides fragilis (P less than 0.001) in the colon. There was no correlation between the diameter of the lesion being resected with the numbers of bacteria in the colon even when oral neomycin and metronidazole were added to the bowel preparation.