Investigation on Constitution of Cytolethal Distending Toxin Gene in Some Intestinal Bacteria and Cell Toxicity thereof

Objective To investigate the constitution of cytolethal distending toxin(CDT) in Escherichia coli strains,Shigella strains and part of Enterobacteriaceae strains,and the cell toxicity thereof.Methods The presence of cdt gene was tested by polymerase chain reaction(PCR),and preliminary evaluation of the expression of CDT toxin and the toxicity thereof were performed by the observation of changes in cell morphology through co-incubation of supernatant of positive strain culture and Hela cells.Results Cdt gene was found in 7 including 3 cdt-Ⅲ and 4 cdt-Ⅰ strains from 43(16.28%) E.coli O157∶NM strains,4 from 150(2.67%) Shigella reference strains and 5 from 80(6.25%) E.coli strains harboring high pathogenicity island of Yersinia enterocolitica,but not found in other members of Enterobacteriaceae,such as Salmonella and Citrobacter.All 16 cdt-positive strains produced active CDT which was evidenced by a progressive distension in Hela cells for up to 4 days after exposure to culture filtrates of the cdt-positive strains.The CDT titres ranged from 1∶2 to 1∶16.Conclusion The data indicate that cdt is present with lower frequency by test only in E.coli O157∶NM,Shigella and high pathogenicity island of Yersinia enterocolitica-harboring E.coli.However,further studies are required to evaluate the relevance of the presence of cdt and severity of the disease,as well as the mechanism of CDT cell toxicity.