Clostridium difficile 027/BI/NAP1 encodes a hypertoxic and antigenically variable form of TcdB

Area of Science:

• Microbiology
• Immunology
• Pathogen Biology

Background:

• Clostridium difficile is a significant pathogen, with its major virulence factor, toxin B (TcdB), exhibiting strain-specific variations.
• Understanding these variations is crucial for developing effective countermeasures against C. difficile infections.

Purpose of the Study:

• To compare the lethality, pathogenicity, and antigenic properties of TcdB from the epidemic BI/NAP1/027 strain (TcdB027) with a previously characterized strain (TcdB003).
• To investigate the impact of sequence variations on toxin neutralization and vaccine development.

Main Methods:

• Mouse intoxication assays were used to determine the lethal dose and observe pathological effects.
• Solid-phase humoral mapping was employed to analyze and compare the antigenic epitopes of TcdB027 and TcdB003, focusing on the carboxy-terminal domains (CTD).
• The protective efficacy of a toxoid vaccine against TcdB027 was assessed.

Main Results:

• TcdB027 was at least fourfold more lethal than TcdB003 in mouse models.
• TcdB027 induced a novel brain hemorrhage in mice, linked to increased sensitivity of brain microvascular endothelial cells.
• Significant antigenic differences were observed between TcdB027 and TcdB003, with reduced cross-neutralization by antibodies targeting the CTD.
• A toxoid form of TcdB027 elicited a strong protective immune response despite epitope variations.

Conclusions:

• TcdB from the BI/NAP1/027 C. difficile strain is a more potent toxin with distinct pathogenic effects, including brain hemorrhage.
• Sequence variations in TcdB alter antigenic epitopes, impacting antibody-mediated neutralization.
• Despite antigenic differences, a toxoid vaccine approach shows promise for protection against TcdB027.