Abstract
Vibrio cholerae causes a severe diarrhoeal disease by secreting a toxin during colonization of the epithelium in the small intestine. Whereas the initial steps of the infectious process have been intensively studied, the last phases have received little attention. Confocal microscopy of V. cholerae O1-infected rabbit ileal loops captured a distinctive stage in the infectious process: 12 h post-inoculation, bacteria detach from the epithelial surface and move into the fluid-filled lumen. Designated the “mucosal escape response,” this phenomenon requires RpoS, the stationary phase alternative sigma factor. Quantitative in vivo localization assays corroborated the rpoS phenotype and showed that it also requires HapR. Expression profiling of bacteria isolated from ileal loop fluid and mucus demonstrated a significant RpoS-dependent upregulation of many chemotaxis and motility genes coincident with the emigration of bacteria from the epithelial surface. In stationary phase cultures, RpoS was also required for upregulation of chemotaxis and motility genes, for production of flagella, and for movement of bacteria across low nutrient swarm plates. The hapR mutant produced near-normal numbers of flagellated cells, but was significantly less motile than the wild-type parent. During in vitro growth under virulence-inducing conditions, the rpoS mutant produced 10- to 100-fold more cholera toxin than the wild-type parent. Although the rpoS mutant caused only a small over-expression of the genes encoding cholera toxin in the ileal loop, it resulted in a 30% increase in fluid accumulation compared to the wild-type. Together, these results show that the mucosal escape response is orchestrated by an RpoS-dependent genetic program that activates chemotaxis and motility functions. This may furthermore coincide with reduced virulence gene expression, thus preparing the organism for the next stage in its life cycle.
Highlights
Vibrio cholerae, an autochthonous microbe of aquatic ecosystems, causes an illness characterized by infection of the small bowel and the production of liquid stools
The actin-rich epithelial surface was stained with phalloidin and is shown with red color, while green fluorescent protein (GFP)-tagged V. cholerae are shown with green color
V. cholerae has previously been shown to move through the mucus gel and attach to the epithelial surface during the first 8 h of infection in the rabbit ileal loop model (Figure 1 and [1,2])
Summary
An autochthonous microbe of aquatic ecosystems, causes an illness characterized by infection of the small bowel and the production of liquid stools. Diarrhea occurs when the volume of the fluid produced exceeds the absorptive capacity of the small bowel and colon. The initial steps of the infectious process, colonization of the small bowel and induction of the virulence program, have been the subject of many reports. The later steps, characterized by detachment of bacteria from epithelial surfaces and their movement into the fluid-filled lumen of the bowel, have received comparatively little attention, even though this is seemingly crucial for the organism’s dissemination to other hosts and environmental sites
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