Prevalence and characterization of cdt genes coding for ADP-ribosylating binary toxin in Clostridium difficile

Abstract

Pathogenicity of Clostridium difficile is often associated with production of toxins A and B, which are encoded by tcdA and tcdB respectively, resulting in diarrhea and pseudomembranous colitis. Another virulence factor, ADP-ribosylating binary toxin (encoded by cdt genes) was recently identified in this organism and may play a role in the pathogenicity. cdt operon was previously reported to be found in 12% of pathogenic clinical isolates. Screening of 110 clinical isolates from Singapore showed that none of them contains the complete cdt genes. However, 40% of the strains harbor the truncated cdt gene variant, suggesting that strains with cdt genes are confined to certain geographical area. In our study, cdt genes were found to expressed as biscistronic transcript in vivo and it could be detected at early log phase of Clostridium difficile growth. Lastly, the transcription start site, putative promoter region and the termination specific sequences of cdt operon were identified.