Cross-protective immunity and the serological classification system for Bacteroides nodosus

Area of Science:

• Veterinary Microbiology
• Immunology
• Bacteriology

Background:

• Ovine footrot is a contagious disease caused by Bacteroides nodosus.
• Serological classification of Bacteroides nodosus is crucial for understanding disease spread and developing effective vaccines.
• Cross-protection between bacterial subgroups is essential for broad-spectrum vaccine efficacy.

Purpose of the Study:

• To investigate the relationship between serological classification systems for Bacteroides nodosus serogroups B and H.
• To examine the extent of cross-protection between subgroups within these serogroups.
• To evaluate the efficacy of pili versus whole cell vaccines in inducing cross-protection.

Main Methods:

• Serological classification of Bacteroides nodosus strains.
• Vaccination of sheep with pili or whole cell vaccines.
• Assessment of protection against challenge with homologous and heterologous subgroup strains.
• Measurement of antibody titres to shared pilus antigens.

Main Results:

• Vaccination induced protection against heterologous subgroup strains when shared pilus antigens elicited sufficient cross-reactive antibodies.
• A pili vaccine provided better cross-protection within serogroup B compared to a whole cell vaccine, correlating with higher pilus antibody titres.
• Serogroup H demonstrated a lack of cross-protection and serological reactivity between subgroups.

Conclusions:

• Shared pilus antigens are critical for cross-protection within Bacteroides nodosus serogroup B.
• The lack of cross-protection within serogroup H suggests that the prototype strain of subgroup H2 warrants designation as a new serogroup.
• Pili vaccines may offer superior cross-protection against ovine footrot compared to whole cell vaccines.