Variant toxin B and a functional toxin A produced by Clostridium difficile C34.

Area of Science:

• Microbiology
• Cell Biology
• Toxicology

Background:

• Clostridium difficile is an opportunistic pathogen known for producing toxins that cause disease.
• The toxins TcdA and TcdB are key virulence factors, but their specific cellular targets and effects are still being elucidated.
• Strain C34 of Clostridium difficile possesses unique genetic features, including an insertion in the tcdA gene.

Purpose of the Study:

• To investigate the functional consequences of a genetic insertion in Clostridium difficile strain C34's tcdA gene.
• To characterize the cytopathic effects and substrate specificities of TcdA-C34 and TcdB-C34.
• To determine the role of specific GTPases in the observed cytopathic effects.

Main Methods:

• Analysis of the tcdA-C34 gene insertion and its impact on TcdA-C34 expression and activity.
• Induction of cytopathic effects (D-type and S-type) in eukaryotic cells using purified toxins.
• Inactivation assays using purified toxins to identify their GTPase substrates.

Main Results:

• An insertion in the tcdA-C34 gene did not prevent the expression of an active TcdA-C34 molecule.
• TcdA-C34 induced a D-type cytopathic effect (arborized appearance), inactivating Rho, Rac, Cdc42, and Rap GTPases.
• TcdB-C34 induced an S-type cytopathic effect (spindle-like appearance), inactivating Rho, Rac, Cdc42, Rap, Ral, and R-Ras GTPases.

Conclusions:

• Clostridium difficile strain C34 coexpresses a D-type enterotoxin (TcdA-C34) and an S-type cytotoxin (TcdB-C34).
• TcdB-C34 is identified as the first S-type cytotoxin that inactivates both Rho and R-Ras GTPases.
• R-Ras GTPase is crucial for the S-type cytopathic effect, which appears to dominate over the D-type effect.