Part of the tripartite complex that is required for the CDT activity. CdtB exhibits a DNA-nicking endonuclease activity, and very probably causes DNA damage in intoxicated cells. This damage induces G2/M cell cycle arrest, chromatin fragmentation, cell distention and nucleus enlargement. Heterotrimer of 3 subunits, CdtA, CdtB and CdtC. Localized to the nucleus of the infected cells. The operon of the strain O128:H- / 9142-88 / EPEC is referred to as cdt type II (CDT-II).