PCR for Detection of cdt-IIIand the Relative Frequencies of Cytolethal Distending Toxin Variant-Producing Escherichia coliIsolates from Humans and Cattle

ABSTRACTA PCR assay that uses primers whose sequences were obtained from the published sequence of the cdt-IIIgene was developed to determine the frequencies of the cdt-I, cdt-II, and cdt-IIIgenes in Escherichia coliisolates from humans and animals. E. coliisolates producing cytolethal distending toxin (CDT) were infrequently detected. The cdt-Igene was preferentially detected in strains with the cnf1gene, while the cdt-IIIgene was found in strains carrying the cnf2gene. The cdt-IIIgenotype was more prevalent in animal isolates, while the cdt-Iand cdt-IIgenotypes were more evident in human isolates. The presence of further cdtgene variants was indicated by the presence of toxin activity in cell culture in the absence of PCR amplification of the cdt-I, cdt-II, or cdt-IIIgene.