Cholera toxin differentially regulates nitric oxide synthesis, tumor necrosis factor-alpha production and respiratory burst in murine macrophages

Upregulation of human mitochondrial NADH dehydrogenase subunit 5 in intestinal epithelial cells is modulated byVibrio choleraepathogenesis

Cholera still remains an important global predicament especially in India and other developing countries. Vibrio cholerae, the etiologic agent of cholera, colonizes the small intestine and produces an enterotoxin that is largely responsible for the watery diarrheal symptoms of the disease. Using RNA arbitrarily primed PCR, ND5 a mitochondria encoded subunit of complex I of the mitochondrial respiratory chain was found to be upregulated in the human intestinal epithelial cell line Int407 following exposure to V. cholerae. The upregulation of ND5 was not observed when Int407 was infected with Escherichia coli strains. Incubation with heat-killed V. cholerae or cholera toxin or culture supernatant also showed no such upregulation indicating the involvement of live bacteria in the process. Infection of the monolayer with aflagellate non-motile mutant of V. cholerae O395 showed a very significant (59-fold) downregulation of ND5. In contrast, a remarkable upregulation of ND5 expression (200-fold) was observed in a hyperadherent icmF insertion mutant with reduced motility. V. cholerae cheY4 null mutant defective in adherence and motility also resulted in significantly reduced levels of ND5 expression while mutant with the cheY4 gene duplicated showing increased adherence and motility resulted in increased expression of ND5. These results clearly indicate that both motility and adherence to intestinal epithelial cells are possible triggering factors contributing to ND5 mRNA expression by V. cholerae. Interestingly infection with insertion mutant in the gene coding for ToxR, the master regulator of virulence in V. cholerae resulted in significant downregulation of ND5 expression. However, infection with ctxA or toxT insertion mutants did not show any significant changes in ND5 expression compared to wild-type. Almost no expression of ND5 was observed in case of mutation in the gene coding for OmpU, a ToxR activated protein. Thus, infection of Int407 with virulence mutant strains of V. cholerae revealed that the ND5 expression is modulated by the virulence of V. cholerae in a ToxT independent manner. Although no difference in the mitochondrial copy number could be detected between infected and uninfected cells, the modulation of the expression of other mitochondrial genes were also observed. Incidentally, upon V. cholerae infection, complex I activity was found to increase about 3-folds after 6 h. This is the first report of alteration in mitochondrial gene expression upon infection of a non-invasive enteric bacterium like V. cholerae showing its modulation with adherence, motility and virulence of the organism.

Role of mast cells and pro-inflammatory mediators on the intestinal secretion induced by cholera toxin

Recent data suggest that diarrhea caused by Vibrio cholerae involves a pro-inflammatory mediators release, such as cytokines, prostaglandin and nitric oxide. The aim of this study was to investigate the role of mast cells and their mediators in the intestinal secretion induced by cholera toxin. We examined the dose responses, time course and role of mast cells and pro-inflammatory mediators in cholera toxin intestinal secretory response, in vivo. Cholera toxin caused a dose-dependent secretion, in ligated small intestine loops, at 18 h. Rats treated with 48/80 compound or ketotifen had a significant decrease in the intestinal secretory response. Cholera toxin secretion was significantly reduced by an unspecific histamine/serotonin receptor antagonist, histamine receptor antagonist, phospholipase A2 and cyclooxygenase inhibitors, platelet-activating factor (PAF) receptor antagonists and TNF-alpha synthesis blockers. On the other hand, pretreatment with a specific serotonin receptor antagonist and lipoxygenase inhibitors failed to block this effect. Analysis of the intestinal fluid from rats injected with cholera toxin, revealed that cholera toxin induces the release of IL-1beta and TNF-alpha into fluid. The data suggest that, at least in part, mast cells are involved in cholera toxin-induced secretion, as well as point to the importance of histamine, prostaglandins, PAF, IL-1beta and TNF-alpha in this process.

Oxygen-utilizing reactions and symbiotic colonization of the squid light organ by Vibrio fischeri

A major goal in microbiology is to understand the processes by which bacteria successfully colonize host tissue. Although a wealth of studies focusing on pathogenic microorganisms has revealed much about the rare interactions that result in disease, far less is known about the regulation of the ubiquitous, long-term, cooperative associations of bacteria with their animal hosts.