In vivo Pathogenicity and Sporulation Patterns of Clostridium difficile.

Abstract

Clostridium difficile infection (CDI) is one of the most commonly reported hospital-associated infections in the U.S., causing to around 500,000 infections and 29,000 deaths each year. This dissertation describes the results of three different studies exploring the role of the host and pathogen on CDI severity. For the first study, 200 successive CDI positive stool samples were collected from the Microbiology Laboratory at Saint Joseph Mercy Hospital. Fecal toxin, spore, and Candida albicans levels were quantified to characterize the in vivo association between toxin and spore levels and whether this association was modified by C. albicans. Results indicate a strong association between toxin and spore levels within the human CDI host, with the association varying by ribotype. C. albicans overgrowth did not modify this association. We next performed a case-control study comparing 120 toxin positive CDI and 91 toxin negative PCR positive CDI hospitalized patients. We described clinical and epidemiological differences between CDI patients according to their laboratory diagnosis. In a population with 92% CDI treatment rate, we confirmed a milder CDI presentation and lower 30-days risk of mortality among toxin negative PCR positive patients. Furthermore, spore levels were associated with CDI severity. These results highlight a major limitation of using PCR in the CDI laboratory algorithm and the importance of the severity of the patient’s clinical presentation when considering treatment for a patient testing as toxin negative PCR positive. Lastly, we used an in-host mathematical model to characterize the role of sporulation/germination patterns on risk of recurrence and compare the effectiveness of several current tapered/pulsed vancomycin regimens on risk of recurrence by specific ribotypes. Our results confirm the importance of C. difficile ribotype in explaining CDI recurrence rates and the effectiveness of treatment. All of the evaluated treatment regimens for repeated CDI were effective; further, regimens with reduced duration or dosage of treatment were still highly effective, suggesting that vancomycin regimens may be modified to a lower level that better protects gut microbiota while preventing CDI recurrence.