The effect of bile on the expression of cholera toxin (CT) and the major subunit of the toxin-coregulated pilus (TcpA) and on motility was examined in the Vibrio cholerae O1 classical-biotype strains O395 and 569B. Although the motility of the cells increased significantly in the presence of bile, transcription of the ctxAB genes, encoding CT, and of the tcpA gene was drastically reduced. In toxR mutant strains, motility is higher than in the wild-type strain and was further increased, by about 150%, in the presence of bile. Bile represses CT production in strain 569B-55, a toxR mutant of strain 569B, which normally produces more than 80% of the amount of CT synthesized in the wild-type cells. These results suggest that bile may target some factor other than ToxR that is involved in the regulation of CT production and motility. Bile has no effect on the relative amounts of the two outer membrane porins, OmpU and OmpT, which are under ToxR control.
Gram-negative bacteria are inherently impermeable to hydrophobic compounds, due to the synergistic activity of the permeability barrier imposed by the outer membrane and energy dependent efflux systems. The gram-negative, enteric pathogen Vibrio cholerae appears to be deficient in both these activities; the outer membrane is not an effective barrier to hydrophobic permeants, presumably due to the presence of exposed phospholipids on the outer leaflet of the outer membrane, and efflux systems are at best only partially active. When V. cholerae was grown in the presence of bile, entry of hydrophobic compounds into the cells was significantly reduced. No difference was detected in the extent of exposed phospholipids on the outer leaflet of the outer membrane between cells grown in the presence or absence of bile. However, in the presence of energy uncouplers, uptake of hydrophobic probes was comparable between cells grown in the presence or absence of bile, indicating that energy-dependent efflux processes may be involved in restricting the entry of hydrophobic permeants into bile grown cells. Indeed, an efflux system(s) is essential for survival of V. cholerae in the presence of bile. Expression of acrAB, encoding an RND family efflux pump, was significantly increased in V. cholerae cells grown in vitro in the presence of bile and also in cells grown in rabbit intestine.Vibrio cholerae, a noninvasive enteric bacterium, is the causative agent of the diarrheal disease cholera. Cholera remains a major cause of human mortality in developing countries, where conditions of poor sanitation, war, famine, and malnourishment contribute to regular episodes of cholera epidemics. For successful infection of its human host, V. cholerae must colonize the small intestine and produce copious amounts of cholera toxin (CT), a potent enterotoxin that causes the massive fluid loss characteristic of the disease. In addition to obvious virulence factors like CT, other toxins, toxin-coregulated pilus, hemolysins, and hemagglutinins (factors essential for survival of the bacteria in vivo and evasion of the host defense system) also contribute to the pathogenecity of V. cholerae (for a review, see references 12 and 24).Enteric pathogens and normal intestinal flora must necessarily survive and colonize the intestine in the presence of bile. Bile salts are surface-active, amphipathic compounds with pronounced detergent-like activity that can cause disaggregation of the lipid bilayer structure of cellular membranes (11). However, gram-negative enteric bacteria are inherently resistant to bile, partly due to the basic, asymmetric structure of their outer membranes (OMs). Although the inner surface of the OM contains phospholipids, a characteristic lipopolysaccharide (LPS) is present on the outer leaflet that significantly retards diffusion of hydrophobic compounds across the OM. The OM thus functions as an effective permeability barrier and gives protection to enteric bacteria from potentially noxious agents present in the intestine, particula...
Almost two thirds of the world population consume tea everyday. Tea is processed differently in different parts of the world to give green (20%), black (78%) or oolong tea (2%). The antimutagenic and anticarcinogenic activities of green tea were extensively investigated compared with those of black tea. Considering the potent antimutagenic effects of green tea we recognized the need to evaluate the antimutagenic effects of black tea (World Blend Tea, Southern Tea Co., Marietta, GA) in Salmonella strains TA97a, TA98, TA100 and TA102 in preincubation tests, both with and without S9 activation. Attempts have also been made to compare the results of the tea extracts with their two active polyphenols theaflavins and thearubigins. Antimutagenicity assays were carried out in bacterial plates treated with different concentrations (1%, 2.5%, 5%, 10% and 20%) of tea extracts against known bacterial mutagens sodium azide, 4-nitro-o-phenylenediamine, cumine hydroperoxide, 2-aminofluorene and danthron. A significant decrease in the number of revertant colonies was observed in the plates treated with 1% to 20% of tea extract plus positive mutagen when compared with positive mutagen only. Both the active polyphenols theaflavins and thearubigins extracted from the black tea (World blend) also showed significant antimutagenic effects against known positive compounds in these strains. In the experiments with S9 activation, the antimutagenic effects were significantly higher. These results indicate that black tea and its two polyphenols have significant antimutagenic effects in Ames Salmonella assays.
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