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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.

Gastric aspirates were obtained from 12 healthy volunteers, 49 patients with duodenal ulcer, 14 with gastric ulcer and 35 with gastric carcinoma. The mean total viable bacterial counts in these groups were as follows: volunteers 0, duodenal ulcer 3.8 X 10(1), gastric ulcer 6.95 X 10(4), carcinoma 1.9 X 10(7) organisms/ml. The incidence of wound sepsis in patients without antibiotic cover was; duodenal ulcer 17 per cent, gastric ulcer 38 per cent, carcinoma 56 per cent. Regardless of the underlying pathology, patients with counts greater than 5 X 10(6) organisms/ml in the gastric aspirate had a 93 per cent incidence of wound sepsis, compared with 16 per cent in patients with counts of less than 5 X 10(6) organisms/ml (P less than 0.001). In the group with high counts all except one of the wound infections were caused by organisms present in the stomach at the time of operation. There was a good correlation in the bacteriology of apirates obtained during preoperative endoscopy compared with operative nasogastric samples (n = 31) both for viable counts (r = 0.93) and for the counts of individual organisms. Therefore, preoperative endoscopy can be used to identify patients who are at risk of developing wound sepsis after gastric surgery.

The influence on colonic microflora of neomycin and metronidazole alone, or in combination, was studied in volunteers taking a normal diet. Bacterial counts on daily faecal samples revealed that metronidazole had no influence on anaerobic faecal bacteria. Neomycin on the other hand, was effective against sensitive aerobes. However, the combination of neomycin and metronidazole profoundly reduced both aerobic and bacteria. Assay of faecal antibiotic concentrations showed that neomycin achieved high intraluminal levels while metronidazole was undetectable or present at low concentrations.