Identification of cdtB homologues and cytolethal distending toxin activityin enterohepatic Helicobacter spp.

A bacterial toxin that causes progressive distension and death of Chinese h amster ovary (CHO) cells and HeLa cells termed cytolethal distending toxin (Cdt), has been identified in several diarrhoeagenic bacteria, including Ca mpylobacter spp. (C. jejuni and C. coli), some pathogenic strains of Escher ichia coli and Shigella spp. Genes encoding this toxin were identified as a cluster of three adjacent genes cdtA, cdtB and cdtC. Homologues of cdtB fr om five species of enterohepatic helicobacters (Helicobacter hepaticus, H. bilis, H. canis and two novel Helicobacter spp. isolated from mice and wood chuck, respectively) were identified by means of degenerative PCR primers, cloned and sequenced. The similarities of these partial cdtB nucleotide seq uences from these Helicobacter spp, to those of cdtB genes known to be pres ent in other bacteria were: C. jejuni, 58.3-64.8%; E. coli, 52.3-57.8%, Hae mophilus ducreyi, 53.4-58.4% and Actinobacillus actinomycetemcomitans, 52.7 -58.1%. Bacterial lysates from four of these helicobacters caused character istic cytolethal distension of HeLa cells. Cdt caused cell cycle arrest at G(2)/M phase as measured by flow cytometry. The results demonstrated the pr esence of a toxin in these Helicobacter spp. belonging to the family of Cdt .