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

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