Enterotoxicity of a nonribosomal peptide causes antibiotic-associated colitis

Abstract

Antibiotic therapy disrupts the human intestinal microbiota. In some patients rapid overgrowth of the enteric bacterium Klebsiella oxytoca results in antibiotic-associated hemorrhagic colitis (AAHC). We isolated and identified a toxin produced by K. oxytoca as the pyrrolobenzodiazepine tilivalline and demonstrated its causative action in the pathogenesis of colitis in an animal model. Tilivalline induced apoptosis in cultured human cells in vitro and disrupted epithelial barrier function, consistent with the mucosal damage associated with colitis observed in human AAHC and the corresponding animal model. Our findings reveal the presence of pyrrolobenzodiazepines in the intestinal microbiota and provide a mechanism for colitis caused by a resident pathobiont. The data link pyrrolobenzodiazepines to human disease and identify tilivalline as a target for diagnosis and neutralizing strategies in prevention and treatment of colitis.bacteria | enteric microbiota | cytotoxin

The Toxin-Producing Pathobiont Klebsiella oxytoca Is Not Associated with Flares of Inflammatory Bowel Diseases

“…In the control group of healthy carriers, four of 12 isolates were toxin-producing, a finding that we have already described in a previous study on antibiotic-associated diarrhea [17,25]. Although disruption of the epithelial barrier by the K. oxytoca cytotoxin tilivalline [18], which in turn can lead to increased exposure to bacterial antigens and activation of the immune system in IBD patients, seems as an attractive hypothesis for causes of IBD flares, our results suggest that this mechanism is very unlikely in most IBD patients. Genetic typing of K. oxytoca stool isolates from IBD patients and controls using MLST yielded 33 distinct sequence types.…”

“…The cytotoxic effects were assessed by microscopic examination (cell rounding and cell death) and quantitative colorimetry (MTT tetrazolium method) as described previously [25]. Furthermore, all strains were tested for the presence of the tilivalline pathogenicity island by PCR amplification of npsB and the intergenic region between npsA and aroX [18].…”

“…The molecular mechanism of how K. oxytoca induces colitis has been identified recently. Colitisinducing strains of K. oxytoca were shown to produce a low-molecular-weight cytotoxin called tilivalline [18]. Tilivalline is a member of the pyrrolobenzodiazepine (PBD) family [18].…”

“…Colitisinducing strains of K. oxytoca were shown to produce a low-molecular-weight cytotoxin called tilivalline [18]. Tilivalline is a member of the pyrrolobenzodiazepine (PBD) family [18]. Other naturally occurring PBDs are selective DNA-alkylating agents with remarkable cytotoxic activity.…”

“…Therefore, tilivalline is the only PBD that is produced in the human intestinal microbiota that is currently known. Tilivalline disrupts the intestinal epithelial barrier via induction of apoptosis and thereby lowers epithelial resistance [18]. The disruption of epithelial barrier functions is thought to be one of the first steps in IBD pathogenesis [8].…”