Mutation in tcpR gene (Vc0832) of Vibrio cholerae O1 causes loss of tolerance to high osmolarity and affects colonization and virulence in infant mice

Abstract

Vibrio cholerae, the agent of cholera, multiplies and colonizes human intestinal tract where it survives high osmolarity due to bile and other sodium salts. In this work, by TnphoA mutagenesis, a mutant of V. cholerae O1 which could not grow and form colonies on LB agar containing 400 mM NaCl has been characterized. The mutant, designated CD83, adhered normally to freshly isolated rabbit intestinal discs, colonized poorly the gut of infant mice and was avirulent in the same model, whereas the parent strain CD81 would colonize the gut and cause death of mice. Attenuation of virulence of CD83 was not attributable to its inability to produce cholera toxin, as no difference was found in the cholera toxin produced in vitro by the mutant and parent strains. Molecular cloning and sequencing of the mutated gene revealed that insertion of transposon occurred in tcpR gene (Vc0832) of V. cholerae. Complementation of the mutant with wild-type tcpR gene resulted in restoration of the ability to survive at high salt concentration (400 mM NaCl), and to colonize the gut and restore virulence. The results suggest that tcpR plays a role in survival of V. cholerae in the small intestine of host as the osmolarity in the intestinal lumen is thought to be equivalent to 300 mM NaCl or higher.

TheSalmonella entericaSerotype Typhi Vi Capsular Antigen Is Expressed after the Bacterium Enters the Ileal Mucosa

“…Vi-suppressing conditions (300 mM NaCl) encountered in the intestinal lumen (13,30,45) are difficult to mimic using tissue culture models, which rely on the use of tissue culture media containing 150 mM NaCl (Fig. 3).…”

“…One hypothesis predicts that osmolarity may represent an important signal for the transition of S. Typhi from the lumen into intestinal tissue (36). In the intestinal lumen, the osmolarity is high, with values considered to be equivalent to 300 mM NaCl and greater (13,30,45). Once S. Typhi invades the intestinal bar-rier, it encounters a lower-osmolarity condition equivalent to ϳ150 mM (29), which has been reported to be the osmolarity of blood and plasma.…”

The Superintegron Integrase and the Cassette Promoters Are Co-Regulated in Vibrio cholerae

“…In parallel, Na+ ions are also secreted into the small intestine [40]. As a consequence, after cholera toxin production [45], NaCl reaches high concentrations inside the intestine (> 300 mM) [46]. Thus, this coincides with the highest expression of the Pc proximal cassettes, and one can imagine that this gives a chance for the massively excreted bacteria to be better fit for the external unpredictable environment in which they will be released.…”

Efficient responses to host and bacterial signals duringVibrio choleraecolonization

“…70,71 Furthermore, mutations in tcpR (a gene in the same operon as the pilus-colonizing factor TCP) results in a loss of tolerance to high osmolarity, defects in colonization, and attenuation of virulence, suggesting that this gene may be at least partially responsible for virulence in vivo. 72 A more recent study looking for changes in the transcriptional profile of bacteria grown in various NaCl concentrations revealed that large classes of genes (including those involved in pathogenesis, biofilm formation, exopolysaccharide synthesis, and solute transport) are differentially regulated in response to salt. A novel transcriptional regulator, OscR, whose expression is downregulated in response to increasing NaCl levels, was also identified in this study.…”