The transmission of Vibrio cholerae is antagonized by lytic phage and entry into the aquatic environment.

摘要

Understanding the transmission of cholera has importance for public health officials attempting to provide sanitation in a resource-scarce environment, and for the vaccinologist attempting to improve vaccine efficacy. Vibrio cholerae is the etiologic agent of the diarrheal disease cholera. V. cholerae is a facultative pathogen that resides in the environment, and on occasion, finds its way into the human host where the actions of cholera toxin cause devastating dehydration and mortality rates that reach 40%. With simple rehydration therapy, mortality rates drop below 1%. Three critical factors affect, or are likely to affect, transmission: (i) the culturability of V. cholerae in the aquatic environment, (ii) the increased infectivity of in vivo derived V. cholerae, and (iii) lytic vibriophage that prey on V. cholerae. The first goal of this thesis was to quantify these factors upon passage from the human host into the aquatic environment. The second goal was to assess the relevance of any one factor in relation to the other factors. The data reveal a model for transmission that pertains to events inside and outside the human host. Inside the host, the model suggests that V. cholerae multiply in the small intestine to produce a fluid niche that is dominated by V. cholerae. If lytic phage are present, culturable counts of V. cholerae drop, and other microorganisms bloom. Outside, in the pond water, the model suggests that a loss of culturable cells (for reasons independent of phage) and a rise of lytic phage block transmission. Thus, there is a fitness advantage if V. cholerae can make a rapid transfer to the next host before these negative selective pressures compound in the aquatic environment. Future research on rice-water stools that harbor both low titers (included in this work) and high titers (not included) of phage will provide further understanding of the impact of lytic phage on transmission. The model proposed herein is supported by epidemiological findings that suggest if an index cholera case passes lytic phage in his/her stool (assayed by darkfield microscopy as a proxy for lytic phage) household contacts are at a decreased risk of being infected with V. cholerae. These findings should provide public health officials with a renewed sense of urgency and an opportunity for sanitary interventions. In terms of vaccine development, transcriptional analysis traced the transformation of V. cholerae as the bacteria passage from patients into the aquatic environment. The nature of the final transcriptome in pond water was a function of the source from which the cells were derived. This finding is important to the vaccinologist because producing a vaccine with 'environmental' antigens from in vitro derived bacteria may not yield the same 'environmental' antigens from patient derived bacteria. Therefore, a vaccine that has antigens relevant to those expressed by V. cholerae in the natural environment may be more difficult to produce than originally considered. Diarrheal disease continues to be the second most common cause of death among children under 5 years of age globally---it is the leading cause of morbidity. I hope these public health and vaccine-oriented findings find relevance to the poverty stricken households of Bangladesh in the near future.