Transformation-mediated serogroup conversion of Dichelobacter nodosus

Area of Science:

• Veterinary Microbiology
• Bacterial Pathogenesis
• Immunology

Background:

• Dichelobacter nodosus is the primary cause of ovine footrot.
• Type IV fimbriae of D. nodosus are crucial for virulence and are highly immunogenic.
• Fimbrial variation is hypothesized to facilitate immune evasion in D. nodosus infections.

Purpose of the Study:

• To demonstrate that antigenic variation in D. nodosus fimbriae can occur via natural transformation and homologous recombination.
• To investigate the genetic mechanisms underlying fimbrial serogroup switching in D. nodosus.

Main Methods:

• A suicide plasmid carrying the fimA gene from a serogroup G strain was used.
• A serogroup I strain of D. nodosus was converted to serogroup G using the plasmid.
• Western blotting and slide agglutination were employed for serogroup determination.
• Genotyping was performed using two independent methods to confirm the parent strain's genotype.

Main Results:

• Mutant strains successfully produced serogroup G fimbriae, confirmed by Western blotting and slide agglutination.
• Despite the serogroup change, the mutant strains retained the genotype of the original serogroup I parent strain.
• This indicates a phenotypic switch in fimbrial antigen expression without a corresponding genotypic alteration in the fimA gene locus.

Conclusions:

• Antigenic variation in D. nodosus fimbriae is achievable through natural transformation and recombination.
• The findings have significant implications for the development and efficacy of fimbrial vaccines against ovine footrot.
• Benign D. nodosus strains may act as reservoirs for diverse fimbrial antigens, potentially influencing vaccine strategies and disease control.