The Vibrio cholerae Cytolysin Promotes Chloride Secretion from Intact Human Intestinal Mucosa

Abstract

BackgroundThe pathogenicity of the Vibrio cholerae strains belonging to serogroup O1 and O139 is due to the production of virulence factors such as cholera toxin (CT) and the toxin-coregulated pilus (TCP). The remaining serogroups, which mostly lack CT and TCP, are more frequently isolated from aquatic environmental sources than from clinical samples; nevertheless, these strains have been reported to cause human disease, such as sporadic outbreaks of watery diarrhoea and inflammatory enterocolitis. This evidence suggested the possibility that other virulence factor(s) than cholera toxin might be crucial in the pathogenesis of Vibrio cholerae-induced diarrhoea, but their nature remains unknown. VCC, the hemolysin produced by virtually all Vibrio cholerae strains, has been proposed as a possible candidate, though a clear-cut demonstration attesting VCC as crucial in the pathogenesis of Vibrio cholerae-induced diarrhoea is still lacking.Methodology/Principal FindingsElectrophysiological parameters and paracellular permeability of stripped human healthy colon tissues, obtained at subtotal colectomy, mounted in Ussing chamber were studied in the presence or absence of VCC purified from culture supernatants of V. cholerae O1 El Tor strain. Short circuit current (ISC) and transepithelial resistance (RT) were measured by a computerized voltage clamp system. The exposure of sigmoid colon specimens to 1 nM VCC resulted in an increase of ISC by 20.7%, with respect to the basal values, while RT was reduced by 12.3%. Moreover, increase in ISC was abolished by bilateral Cl− reduction.Conclusion/SignificanceOur results demonstrate that VCC, by forming anion channels on the apical membrane of enterocytes, triggers an outward transcellular flux of chloride. Such an ion movement, associated with the outward movement of Na+ and water, might be responsible for the diarrhoea caused by the non-toxigenic strains of Vibrio cholerae.

Role of Pore-Forming Toxins in Bacterial Infectious Diseases

“…Examples of PFTs that directly damage epithelial cells are GAS SLO, S. aureus alpha-toxin (190), B. thuringiensis Cry5B (330), C. perfringens ␤-toxin (77) and ε-toxin (81), and V. cholerae VCC (205,206). Findings in vitro for GAS, B. anthracis, and C. perfringens further support the notion that PFTs induce barrier dysfunction (465)(466)(467).…”

“…Non-O1 and non-O139 serotype V. cholerae strains, which are usually cholera toxin (CT) and toxin-coregulated pilus A (TcpA) negative, can still cause watery diarrhea (205,206). It was found that in such strains VCC induces a CT-like effect on excised human intestine, in that it causes leakage of Cl Ϫ ions, resulting in an outflow of Na ϩ and water (206). Barrier dysfunction in other tissues.…”

Memory T-Cell Responses to Vibrio cholerae O1 Infection

“…The hly gene that encodes the VCC protein is widespread across both pathogenic and environmental strains of V. cholerae, suggesting that VCC may impart an advantage to the organism (42). Although the precise role of VCC in V. cholerae infection is unknown, VCC is the primary virulence factor in V. cholerae infection with non-O1, non-O139 strains that do not produce cholera toxin (12,46). The immune response to VCC is not well understood; however, recent studies suggest that VCC may promote a Th2 response in V. cholerae infection (2).…”

Crystal structure of the Vibrio cholerae cytolysin heptamer reveals common features among disparate pore-forming toxins

“…hemolysin | membrane protein | X-ray crystallography | virulence factor T he devastating human pathogen Vibrio cholerae, which is endemic in many parts of the globe and responsible for thousands of deaths annually, produces a cell-damaging toxin, Vibrio cholerae cytolysin (VCC), that permeabilizes human intestinal and immune cells (1)(2)(3) and significantly facilitates intestinal colonization in mouse models (4). Although VCC's involvement as a virulence factor in the human cholera pandemic remains unclear, this toxin belongs to a much larger class of pore-forming toxins (PFTs) secreted by a wide variety of human pathogens (5).…”