Intestinal bacteria play an important role in the pathogenesis of Crohn’s disease, which occurs at sites with the highest concentrations of bacteria. Adherent invasive Escherichia coli associate with the ileal mucosa in Crohn’s disease,¹ and E coli, Bacteroides, and fusiform bacteria are associated with early disease recurrence after surgical resection.² The incidence of clinical recurrence is approximately 50% at three years, with the risk higher in smokers than non-smokers. Endoscopic recurrence occurs in 73–90% of patients one year after surgery,³ and clinical disease correlates reasonably well with the endoscopic score.⁴ Current postoperative prophylaxis therapies are unsatisfactory. Mesalazine 3 g daily, 6-mercaptopurine 50 mg daily, and azathioprine 2 mg/kg daily are only slightly more effective than placebo.⁵ Antimicrobial agents …