Comparative Genomics and Virulence Mechanisms to Identify Genes Related to Mucin O‐Glycan Degradation and Pathogenicity in a Potentially Multidrug‐Resistant <i>Clostridium tertium</i> Strain

Clostridium tertium is a pathogenic bacterium that directly colonizes the gastrointestinal mucosa, causing inflammation and neutropenia. The virulence factors and pathogenic mechanisms of C. tertium are not well known. In this study, C. tertium HGMC01 was isolated by enrichment culture of human feces, and its whole chromosome genome was sequenced without extra plasmids. C. tertium HGMC01 had a larger genome and a higher gene count compared with five other C. tertium strains. A pangenome analysis of six strains showed that C. tertium HGMC01 had the highest number of unique genes and the lowest number of accessory genes clustered phylogenetically with C. tertium src5, a strain of animal origin. C. tertium HGMC01 genome showed a variety of secreted glycoside hydrolases and carbohydrate-binding modules for mucin O-glycan degradation and sialic acid catabolism including sialidase and sialic acid transporter. These genes strongly suggested that the strain could interact the human gut cells through recognition or adhesion to mucin glycans. Moreover, various mobile genetic elements in its genome also indicated the genetic diversity and plasticity of the strain to gain virulence factors and antibiotic/multidrug-resistant genes potentially acquired by horizontal gene transfer for the evolution of the pathogenicity. Additionally, experiments with human embryonic kidney cells revealed that components of C. tertium HGMC01 cell wall may play roles as virulence factors by modulating cytokine signaling pathways dependent on Toll-like receptors. Overall, this comparative genomic analysis provides information about how C. tertium strains cause disease through mucin glycan degradation, colonization, multidrug resistance, and modulation of immune responses.