Part of the tripartite complex that is required for the CDT activity. CdtC, along with CdtA, probably forms a heterodimeric subunit required for the delivery of CdtB. Heterotrimer of 3 subunits, CdtA, CdtB and CdtC. The operon of the strain O128:H- / 9142-88 / EPEC is referred to as cdt type II (CDT-II).