Intestinal colonization by the enteric pathogens Vibrio parahaemolyticus and Vibrio cholerae

Abstract

The enteric bacterial pathogens Vibrio parahaemolyticus and Vibrio cholerae can access and proliferate within the human intestine. This process, referred to as intestinal colonization, can result in moderate to severe diarrhea. This dissertation presents studies of V. parahaemolyticus and V. cholerae intestinal colonization conducted in an animal model of intestinal colonization and diarrheal disease. The horizontally acquired type III secretion system (T3SS2) was the sole factor known to enable V. parahaemolyticus intestinal colonization. Implementing transposon-insertion sequencing (TIS) identified genes essential for V. parahaemolyticus growth in vitro and additional genes necessary for intestinal colonization. toxR, an ancestral locus in Vibrio species, was required for V. parahaemolyticus fitness in vivo and for induction of T3SS2 gene expression. V. parahaemolyticus ToxR activation of T3SS2 resembled V. cholerae ToxR regulation of distinct virulence elements acquired via lateral gene transfer. Thus, disparate horizontally acquired virulence systems have been placed under the control of this ancestral transcription factor across independently evolved human pathogens. In contrast to V. parahaemolyticus, the factors enabling V. cholerae intestinal colonization have been studied in depth. Knowledge of these factors informed engineering of HaitiV, a live attenuated cholera vaccine candidate. Administering HaitiV 24 hours prior to lethal challenge with wild type V. cholerae reduced intestinal colonization by the wild type strain, slowed disease progression, and reduced mortality in an animal model of cholera-like illness. Protection required viable vaccine, and protection kinetics were not consistent with development of adaptive immunity. These observations suggest that HaitiV mediates probiotic protection from cholera that is distinct from traditional vaccines. This dissertation illustrates how TIS has been implemented in diverse systems, but the absence of approaches to integrate data across multiple studies limits the method’s utility. Comparative TIS, a post-hoc analysis framework allowing for statistically rigorous comparisons of data across TIS studies, was created to overcome this limitation. Comparative TIS revealed genes that enable intestinal colonization for multiple pathogenic Vibrios and genes that exhibit strain-specific intestinal colonization phenotypes. This approach has significant implications for meta-analysis of TIS data and for utilizing TIS data as a readout of complex growth environments.