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We are grateful for Dr. Aspinall’s comments on our paper. We did not intend to imply that Koch’s postulates had been fulfilled by our report of increased numbers of mucosa-associated bacteria in Crohn’s disease and colon cancer. Indeed, it may be difficult to do this, given that there is probably a range of relevant mucosa-associated bacteria, with adhesive E. coli predominantly involved but not uniquely so. The various genetic animal models of inflammatory bowel disease have, however, all been shown to depend on the presence of nonpathogenic bacteria,1Wirtz S. Neurath M.F. Animal models of intestinal inflammation new insights into the molecular pathogenesis and immunotherapy of inflammatory bowel disease.Int J Colorectal Dis. 2000; 15: 144-160Crossref PubMed Scopus (132) Google Scholar, 2Rath H.C. Schultz M. Freitag R. Dieleman L.A. Li F. Linde H.J. Scholmerich J. Sartor R.B. Different subsets of enteric bacteria induce and perpetuate experimental colitis in rats and mice.Infect Immun. 2001; 69: 2277-2285Crossref PubMed Scopus (274) Google Scholar and in one example, the IL-2 deficient mouse, E. coli seems specifically to be involved.3Waidmann M. Bechtold O. Frick J. Lehr H. Schubert S. Dobrindt U. Loeffler J. Bohn E. Autenrieth I.B. Bacteroides vulgatus protects against Escherichia coli-induced colitis in gnotobiotic interleukin-2-deficient mice.Gastroenterology. 2003; 125: 162-178Abstract Full Text Full Text PDF PubMed Scopus (171) Google Scholar, 4Schuppler M. Lotzsch K. Waidmann M. Autenrieth I.B. An abundance of Escherichia coli is harboured by the mucosa-associated bacterial flora of interleukin-2-deficient mice.Infect Immun. 2004; 72: 1983-1990Crossref PubMed Scopus (36) Google Scholar Bacteria have also been shown to be essential for the development of colon cancer in similar animal models.5Engle S.J. Ormsby I. Pawlowski S. Boivin G.P. Croft J. Balish E. Doetschman T. Elimination of colon cancer in germ-free transforming growth factor beta 1-deficient mice.Cancer Res. 2002; 62: 6362-6366PubMed Google Scholar It is certainly possible that the presence of the bacteria in the sub-mucus niche in human Crohn’s disease and colon cancer could have been encouraged by disease-associated changes in the mucosa, indeed the hypothesis which prompted this study was that the disease-associated alterations in mucosal glycosylation found in inflammatory bowel disease and colon cancer might predispose to altered recruitment of bacteria to the mucosa.6Rhodes J.M. Unifying hypothesis for inflammatory bowel disease and related colon cancer sticking the pieces together with sugar.Lancet. 1996; 347: 40-44Abstract Full Text PDF PubMed Scopus (90) Google Scholar The suggestion that bacterial adherence might be a consequence of activation of virulence genes following contact with the inflamed mucosa is interesting but none of the known virulence genes other than adherence genes, were shown to be expressed by the mucosal isolates, moreover the lack of any increase in such bacterial isolates in ulcerative colitis makes it unlikely that this was simply secondary to acute inflammation. The bowel preparation used for colonoscopy was identical for Crohn’s disease patients and controls so seems unlikely to have been an issue. This study shows that close apposition to mucosal cells of E. coli, even those lacking conventional genetic markers of pathogenicity, results in release of pro-inflammatory cytokines. We have shown that cellular invasion by bacteria is not essential to this process. It seems to us highly likely that this inflammatory response plays a part in the inflammation associated with Crohn’s disease and we have previously made the case that similar, albeit lower grade, inflammatory changes might contribute to the risk of sporadic cancer development, mediated probably via inhibition of apoptosis.7Rhodes J.M. Campbell B.J. Inflammation and colorectal cancer inflammatory bowel disease-associated cancer and sporadic cancer compared.Trends Mol Med. 2002; 8: 10-16Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar Although evidence from the gentamicin treatment/cell lysis assay of mucosal biopsies and the parallel studies on epithelial cell lines in culture suggest that cellular invasion occurs we were careful to point out that the invasion of cultured epithelial cells is cell-line dependent and that in human Crohn’s disease tissue intramucosal E. coli have been more convincingly shown within macrophages.8Liu Y. van Kruiningen H.J. West A.B. Cartun R.W. Cortot A. Colombel J.F. Immunocytochemical evidence of Listeria, Escherichia coli, and Streptococcus antigens in Crohn’s disease.Gastroenterology. 1995; 108: 1396-1404Abstract Full Text PDF PubMed Scopus (273) Google Scholar In all cases a positive result of the gentamicin survival assay was supported by confirmation that the same bacterial isolate was susceptible to gentamicin and we did not identify any examples of gentamicin-resistant E. coli. Are adherent Escherichia coli in Crohn’s disease and colon cancer truly pathogenic?GastroenterologyVol. 127Issue 5PreviewThe recent paper by Martin et al. made several interesting observations.1 However, the authors’ statement that their results “support a central role for mucosally adherent bacteria in the pathogenesis of Crohn’s disease and colon cancer” does not fulfill Koch’s postulates, even in the modern molecular era.2 Full-Text PDF