Resea Rch pape R Gut Microbes 3:6, 501-509; November/December 2012; © 2012 Landes Bioscience Resea Rch pape R Genotoxicity of Escherichia coli Nissle 1917 strain cannot be dissociated from its probiotic activity Maïwenn Olier,1,2,3,4,5,* Ingrid Marcq,2,3,4,5 c hristel s alvador-c artier,1 Thomas s echer,2,3,4,5 Ulrich Dobrindt,6 Michèle Boury,2,3,4,5 Valérie Bacquié,1 Marie penary,2,3,4,5 eric Gaultier,1 Jean-philippe Nougayrède,2,3,4,5 Jean Fioramonti1 and eric Oswald2,3,4,5,7,* 1Neuro-gastroenterologie et Nutrition; UMR INRa /eNVT 1331; Toulouse, France; 2INRa ; Usc 1360; Toulouse, France; 3Inserm; UMR1043; Toulouse, France; 4c NRs; UMR5282; Toulouse, France; 5Université de Toulouse; Ups, c entre de physiopathologie de Toulouse purpan (cp Tp); Toulouse, France; 6Universität Münster; Institut für h ygiene; Münster, Germany; 7ch U Toulouse; h ôpital purpan; s ervice de bactériologie-h ygiène; Toulouse, France Keywords: Colibactin, colitis, Escherichia coli, probiotic, genotoxin, inflammation, DSS, CD4+ CD45RBhigh T-cell transfer model Abbreviations: ANOVA, analysis of variance; cfu, colony forming unit; DMEM, Dulbecco’s modified Eagle’s medium; DSS, dextran sodium sulfate; FACS, fluorescence activated cell sorting; FBS, fetal bovine serum; IBD, inflammatory bowel diseases; IEC, intestinal epithelial cells; IL, interleukin; MPO, myeloperoxidase; UC, ulcerative colitis; WT, wild-type Oral administration of the probiotic bacterium Escherichia coli Nissle 1917 improves chronic inflammatory bowel diseases, but the molecular basis for this therapeutic efficacy is unknown. E. coli Nissle 1917 harbors a cluster of genes coding for the biosynthesis of hybrid nonribosomal peptide-polyketide(s). This biosynthetic pathway confers the ability for bacteria to induce DNa double strand breaks in eukaryotic cells. h ere we reveal that inactivation of the clbA gene within this genomic island abrogated the ability for the strain to induce DNa damage and chromosomal abnormalities in non-transformed cultured rat intestinal epithelial cells but is required for the probiotic activity of E. coli Nissle 1917. Thus, evaluation of colitis severity induced in rodent fed with E. coli Nissle 1917 or an isogenic non-genotoxic mutant demonstrated the need for a functional biosynthetic pathway both in the amelioration of the disease and in the modulation of cytokine expression. Feeding rodents with a complemented strain for which genotoxicity was restored confirmed that this biosynthetic pathway contributes to the health benefits of the probiotic by modulating its immunomodulatory properties. Our data provide additional evidence for the benefit of this currently used probiotic in colitis but remind us that an efficient probiotic may also have side effects as any other medication. Introduction Probiotics, when administered alive and in adequate amounts, are supposed to be safe and confer health benefits to the host.1 As they are generally marketed as “natural” cures, probiotics benefit also from a positive public image among patients. Nonetheless, physicians need scientific guidance and additional investigations to definitively state on efficacy of probiotics before they can be routinely recommended in clinical practice.2 Several probiotic bacteria have been identified as promising in the management of inflammatory bowel disease (IBD),3-5 but only few studies identified the mode of action of these bacteria.6-9 A better under- standing of the mechanisms by which probiotics promote health remains critical to fully optimize their safety assessment for human use.10 Escherichia coli Nissle 1917 (Mutaflor®) has been commercially available for almost one century and successfully used in humans as an oral treatment for a number of intestinal disorders.11 A number of studies have shown positive results when this strain is used in conditions such as Crohn disease, pouchitis, irritable bowel syndrome or necrotizing enterocolitis12 but is especially used in the prevention of relapse in patients with ulcerative coli- tis (UC). Double blind randomized controlled trials comparing the efficacy of E. coli Nissle 1917 to that of mesalazine, which is part of the first-line treatment in patients with UC, have shown that E. coli Nissle 1917 is as efficient as mesalazine to prevent relapse of UC.13-15 In addition, the probiotic treatment is associ- ated with a prolonged remission without any reported adverse effects. However, although E. coli Nissle 1917 is one of the best studied probiotic bacterial strains, the genetic determinants gov- erning the probiotic nature of E. coli Nissle 1917 are yet to be elucidated.16,17 We have previously identified in the genome of E. coli Nissle 1917 a cluster of genes named “pks island” that allow production of a hybrid peptide polyketide genotoxin, called Colibactin.18 Up to date, purification of Colibactin has failed and its structure remains unsolved but we previously reported that E. coli strains harboring this pks island are able to induce DNA damage in vivo and trigger genomic instability and gene mutations in mammalian cells.19 Given a possible contribution of Colibactin to the development of sporadic colorectal cancer, we wished to explore whether inactivation of this biosynthetic *Correspondence to: Maïwenn Olier and Eric Oswald; Email: maiwenn.olier@toulouse.inra.fr and eric.oswald@inserm.fr Submitted: 05/24/12; Revised: 07/25/12; Accepted: 08/05/12 http://dx.doi.org/10.4161/gmic.21737 www.landesbioscience.com Gut Microbes 501