Genome sequence and characterization of a hypervirulent BI/NAP1/027 Clostridioides difficile (CDC20121308)

Clostridioides difficile is a gram-positive bacterium implicated in antibiotic-associated diarrhea. The use of antibiotics alters the gut microbiota, rendering the host susceptible to infection by C. difficile. This pathogen colonizes the large intestine of humans and animals leading to asymptomatic carriage or clinical manifestations such as toxic megacolon and fulminant colitis depending on a wide range of pathogen and host factors. The emergence of BI/NAP1/027 strains in North America and the spread of these hypervirulent ribotypes worldwide have been linked to the increase in incidence and severity of C. difficile infections (CDI) over the last decade. In this work, we aimed to characterize the BI/NAP1/027 C. difficile commercial strain CDC20121308 widely employed in the study of host-pathogen interactions.

The genome sequence was obtained using a whole-genome shotgun strategy. A total of 3,717 coding sequences (CDS) and 45 tRNAs were predicted. The annotation of the CDC20121308 strain identified 26% of CDS into RAST subsystems. We also detected the presence of RT 027 lineage markers such as thyA, cdtA, cdtB and tc dC 18bp-deletion. Moreover, the genome of CDC20121308 had 11 genes devoted to resistance to toxic compounds, antibiotics (e.g. Tetracycline (Tet) and Vancomycin (Van)) and disinfecting agents as predicted using CARD. C. difficile CDC20121308 resistance to Van and Tet was confirmed by broth microdilution assay. Crystal violet staining demonstrated biofilm formation, which could be associated with antibiotic resistance and pathogenicity. Additionally, we observed a spreading diffuse growth in soft agar tubes, suggesting a motile phenotype. Lastly, a genomic region containing Type 4 Secretory System components such as virD4, virB4, and virB6 was identified.

In conclusion, our results allowed a genomic and functional characterization of the BI/NAP1/027 C. difficile CDC20121308 strain. We demonstrated the presence of several genes associated with pathogenesis that were validated by experimental assays. This study provides additional data for the use of this highly virulence commercial strain of epidemiological relevance in research works involving in vitro and in vivo approaches.