The Picture of C. difficile epidemic and non-epidemic ribotypes: are there differences in virulence?

The purpose of these studies was to determine if the epidemic ribotype of C. difficile (now Clostridioides difficile) was more virulent than non-epidemic ribotypes, to ascertain whether clinics contribute to community-acquired C. difficile, and to bridge gaps in understanding between C. difficile epidemiology and pathology. Virulence of the epidemic isolates was determined to be greater than non-epidemic isolates within LD50 studies utilizing a hamster model of C. difficile disease. In the epidemic isolates, increased production of toxins A and B, increased spore adherence ability, and increased production of spores when antibiotic treatment was administered were factors that are believed to play a role both in increased virulence and in the ability of the epidemic isolate to persist as epidemic. Our results indicate that primary care clinics have higher frequency of contamination of C. difficile spores than hospitals. The study also revealed that of all the samples positive for C. difficile, approximately 90% contained the genes for toxins A, B or both. Thus, primary care clinics can be a source of C. difficile and contribute to community-acquired C. difficile. However, the epidemic ribotype of C. difficile was not isolated at significantly increased levels compared to non-epidemic ribotypes. This suggests that other factors may contribute to its increased frequency of C. difficile infection diagnosis. Isolates of the epidemic ribotype were found to be more virulent than other non-epidemic isolates in both the hamster and mouse models of CDI. In particular, the epidemic ribotypes of C. difficile had lower LD50 values in hamsters than the non-epidemic isolates. The increased severity of disease was associated with higher levels of toxins A and B, but not the number of organisms recovered. The increased toxin production was observed in both the hamster and mouse models of CDI. In addition, it is believed that increased ability of epidemic isolate spores to adhere to the intestinal epithelium in vitro, and produce more spores when treated with the antibiotic vancomycin in hamsters are also important contributors to the enhanced virulence and prevalence associated with epidemic isolates of C. difficile. This revealed a possible link between C. difficile's epidemiology and pathology, and suggested that this connection can potentially explain how epidemic ribotypes persist as epidemic. Though it is likely that the factors discussed throughout this dissertation play a significant role in the epidemic ribotype's ability to persist as epidemic, it is important to note that there may be other contributing factors, such as those found in the in vivo environment. These other factors should be accounted for during future studies of C. difficile's virulence, as future ribotypes are characterized, and as novel treatments are developed to combat C. difficile infections. Still, it is strongly believed that the findings in this dissertation contribute significantly to understanding why the epidemic ribotype is epidemic, and to exposing virulence characteristics that are contributing to this.