![Enterotoxins are present in vivo during colitis. K. oxytoca aroX- and NRPS-operons produce tilimycin (TM), which reacts spontaneously with indole to form tilivalline (TV). These products are involved in AACH. Endoscopic images of the transverse colons of AAHC patient A with severe edema and a diffuse hemorrhagic mucosa with erosions and a healthy subject. [Adapted from Unterhauser et al. PNAS 2019] Revealed the molecular mechanism of colitis caused by the intestinal bacteria Klebsiella oxytoca](/sites/default/files/2019-02/imagen-web_0.jpg)
The molecular basis of antibiotic-associated hemorrhagic colitis (AAHC) caused by intestinal resident Klebsiella oxytoca have been revealed by an international research team with the collaboration of the group led by Dr. Fernando Díaz at Centro de Investigaciones Biológicas, as published in the journal Proceedings of the National Academy of Sciences (PNAS). The study shows that although the enterotoxins tilivalline and tilimycin produced during colitis outbreak share a pyrrolobenzodiazepine structure, they have distinct molecular targets.
Establishing links between bacterial metabolites and human intestinal disease remains a significant challenge and this work has provided insight in the field by demonstrating that tilivalline and tilimycin produced by colitogenic strains are present in the human intestine during active colitis and their concentrations were determined in a murine disease model. Moreover, the researchers have found that tilimycin acts as a genotoxin activating damage repair mechanisms in cultured cells when interacting with the DNA and causing DNA strand breakage and an increased lesion burden.
On the other hand, the biochemical and cellular experiments performed by Dr. Díaz's group have allowed to elucidate the distinct behavior of tilivallin, which promotes tubulin polymerization and stabilizes microtubules leading to mitotic arrest, as confirmed by immunofluorescence and TEM microscopy. The researchers also observed mitotic abnormalities in cell cultures that corresponded to those expected for microtubule stabilizing agents, although the low amount of tilivallin molecules interacting with tubulin in vitro, suggests a mechanism of action related to GTP-bound-like state of tubulin (such as that found at the growth tip of the microtubules) which differs from the action mechanism of one of the most common stabilizing agents, paclitaxel, that binds tubulin all along the microtubule.
The capacity of both tilimycin and tilivallin toxins to induce apoptosis in intestinal epithelial cells - a hallmark feature of AAHC - by independent modes of action, supports the author’s proposal that these metabolites act collectively in the pathogenicity of colitis and opens a new pathway for future studies.
Reference: Klebsiella oxytoca enterotoxins tilimycin and tilivalline have distinct host DNA damaging and microtubule stabilizing activities. K. Unterhauser, L. Pöltl, G. Schneditz, S. Kienesberger, R. A. Glabonjat, M. Kitsera, J. Pletz, F. Josa-Prado, E. Dornisch, C. Lembacher-Fadum, S. Roier, G. Gorkiewicz, D. Lucena-Agell, I. Barasoain, W. Kroutil, M. Wiedner, J. I Loizou, R. Breinbauer, J. F. Díaz, S. Schild, C. Högenauer, E. L. Zechner. Proceedings of the National Academy of Sciences (PNAS)