Table 1.

The virulence factors in C. difficile and their function.

Virulence Factor	Encoding Genes	Role in CDI	References
Toxin A	tcdA	Multiple cytopathic and cytotoxic effects on the targeted cells include disruption of Rho, Rac and Cdc42-dependent signalling, the actin cytoskeleton and the tight adherence junctions, increasing epithelial permeability, allowing commensal bacterial translocation, inflammation, diarrhoea and sometimes death.	[66,67,68,75]
Toxin B	tcdB
TcdR	tcdR	TcdR is a positive regulator (produced in response environmental conditions) that triggers the induction of transcription of the toxin genes (tcdA and tcdB).	[76,77]
TcdC	tcdC	TcdC is a negative regulator that inhibits the expression of tcdA and tcdB. Mutations may cause increased production of toxins A and B.	[62,64]
TcdE	tcdE	TcdE may function as a lytic protein to facilitate the release of toxins A and B to the extracellular environment by a phage-like system, as these toxins lack signal peptides.	[78,79]
CDT	cdtA & cdtB	C. difficile binary toxin (CDT) is a transferase that disrupts the normal cytoskeletal function of cells by inhibiting the protein actin. The altered actin cytoskeleton causes an imbalance between actin and microtubules.	[69,70,71]