Molecular profile and genetic diversity of cytolethal distending toxin (CDT)-producing Escherichia coli isolates from diarrheal patients

Cytolethal distending toxin (CDT)-producing Escherichia coli strains are considered to be a heterogeneous group of E. coli. In the present investigation, 20 CDT-producing E. coli strains, which had already been shown to be cytotoxic necrotizing factor (cnf) gene positive, were selected by PCR. Since these strains proved to be CDT producers on CHO cells but were partially characterized by PCR, they were subjected to PCR analysis to amplify the complete coding region of cdt genes. Moreover, the genetic relatedness of these strains was examined by pulse field gel electrophoresis (PFGE). To check the extent of homogeneity of these strains at the chromosomal level, tRNA insertion site analysis was performed. The CDT-producing E. coli strains under investigation were shown to be heterogeneous and diverse in regard to their genetic analysis. This observed diversity could be an independent acquisition of virulence genes that might occur through horizontal gene transfer by mobile genetic elements. This conclusion is based on the fact that data shown by tRNA insertion site analysis revealed that there is no common pattern of insertion among these isolates although they do share a common trait of CDT production.