Pathogenicity Locus, Core Genome, and Accessory Gene Contributions to Clostridium difficile Virulence

Area of Science:

• Microbiology
• Infectious Diseases
• Genomics

Background:

• Clostridium difficile (C. diff) causes a spectrum of intestinal infections, from asymptomatic carriage to life-threatening colitis.
• Disease severity is influenced by host factors (age, immunity, microbiome) and potentially by C. diff strain virulence.
• Previous studies inconsistently linked specific C. diff strains to disease severity due to patient variability.

Purpose of the Study:

• To determine the relative in vivo virulence of 33 distinct clinical C. diff strains.
• To identify genetic factors contributing to C. diff virulence and disease severity.

Main Methods:

• Tested 33 clinical C. diff isolates in a standardized mouse model (genetically identical, antibiotic-pretreated).
• Assessed virulence based on lethality and disease severity in infected mice.
• Performed whole-genome sequencing to identify genetic differences between high- and low-virulence strains.

Main Results:

• C. diff clade 2 strains, including those historically associated with severe disease (e.g., ST1/ribotype 027), exhibited higher lethality in mice.
• Mouse-derived disease severity correlated with human-reported disease severity for the tested C. diff strains.
• Strain ability to grow in secondary bile acids, rather than toxin production, correlated with increased disease severity.

Conclusions:

• Strain-specific genetic content, particularly accessory genes, significantly contributes to C. diff virulence and disease severity.
• The mouse model effectively recapitulates human C. diff disease spectrum, enabling virulence comparisons.
• Identifying genetic determinants of C. diff virulence can inform strategies for managing severe infections.