Alkaline pH Increases Swimming Speed and Facilitates Mucus Penetration for Vibrio cholerae

Intestinal mucus is the first line of defense against intestinal pathogens. It acts as a physical barrier between epithelial tissues and the lumen that enteropathogens must overcome to establish a successful infection. We investigated the motile behavior of two strains (El Tor C6706 and Classical O395) in mucus using single-cell tracking in unprocessed porcine intestinal mucus. We determined that can penetrate mucus using flagellar motility and that alkaline pH increases swimming speed and, consequently, improves mucus penetration. Microrheological measurements indicate that changes in pH between 6 and 8 (the physiological range for the human small intestine) had little effect on the viscoelastic properties of mucus. Finally, we determined that acidic pH promotes surface attachment by activating the mannose-sensitive hemagglutinin (MshA) pilus in El Tor C6706 without a measurable change in the total cellular concentration of the secondary messenger cyclic dimeric GMP (c-di-GMP). Overall, our results support the hypothesis that pH is an important factor affecting the motile behavior of and its ability to penetrate mucus. Therefore, changes in pH along the human small intestine may play a role in determining the preferred site for during infection. The diarrheal disease cholera is still a burden for populations in developing countries with poor sanitation. To develop effective vaccines and prevention strategies against , we must understand the initial steps of infection leading to the colonization of the small intestine. To infect the host and deliver the cholera toxin, has to penetrate the mucus layer protecting the intestinal tissues. However, the interaction of with intestinal mucus has not been extensively investigated. In this report, we demonstrated using single-cell tracking that can penetrate intestinal mucus using flagellar motility. In addition, we observed that alkaline pH improves the ability of to penetrate mucus. This finding has important implications for understanding the dynamics of infection, because pH varies significantly along the small intestine, between individuals, and between species. Blocking mucus penetration by interfering with flagellar motility in , reinforcing the mucosa, controlling intestinal pH, or manipulating the intestinal microbiome will offer new strategies to fight cholera.