**3.4. Cytolethal distending toxin (CDT)**

Cytolethal distending toxin, having a unique property of damaging the DNA of the target cell, was first reported in pathogenic *E. coli* in 1987 [28, 42]. This toxin has the ability to arrest the cell cycle and contributes to the pathogenesis of UTIs [43, 44]. However, CDT is an operon product encoding three proteins including CdtA, CdtB, and CdtC proteins which are encoded by cdtA, cdtB, and cdtC genes, respectively [28]. CDT has DNase I-like enzymatic activity and attacks DNA, while the other bacterial toxins attack the cell membrane or different targets within the cytoplasm [45]. This unique property of attacking DNA damages the target cell DNA which results in progressive cell distending leading to cell death [27].
