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Examination of diarrheagenicity of cytolethal distending toxin: suckling mouse response to the products of the cdtABC genes of Shigella dysenteriae

Some strains of Escherichia coli, Shigella spp., and Campylobacter spp. that have been implicated in diarrheal disease produce cytolethal distending toxin (CDT). CDT induces unique morphological changes in Chinese hamster ovary cells, but its association with diarrheal disease is unclear. We studied the diarrheagenicity of CDT using the cdt genes that we originally cloned from Shigella dysenteriae. The cdt genes were subcloned into a high-copy-number plasmid in E. coli JM109 to achieve high-level CDT production into the culture supernatant. An isogenic CDT- derivative was constructed by deletion of the 0.9-kb sequence internal to the cdt genes. A suckling mouse model was established, in which the intragastrically administered culture supernatant of the CDT+ E. coli strain induced excretion of loose and/or watery feces more often than did that of the CDT- strain in 24 h. The partially purified CDT preparation induced profuse watery diarrhea by 12 h in this model. High-level intestinal fluid accumulation in 4 h appeared to be related to the watery diarrhea. The results indicate that CDT is diarrheagenic to suckling mice and suggest that diarrheagenicity is dependent on CDT level. The preparations containing wild-type CDT induced tissue damage (necrosis and reparative hyperplasia) in the descending colon, whereas the tissues of the small intestines remained apparently intact. Association between the colonic damage and diarrhea is unclear and needs further investigation.