Vibrio cholerae

Vibrios are highly motile, curved shaped rods with a single polar flagellum that is used for self-propulsion. Vibrio cholerae is a non-spore-forming, gram-negative, facultative anaerobic bacterium of the family Vibrionaceae. V. cholerae is the causative agent of cholera, which is a diarrhoeal disease of the small intestine. Transmission of V.cholerae to humans occurs via the faecal-oral route and through the ingestion of contaminated water or food (WHO).

There are numerous serogroups of V. cholerae but until 1992 the only vibrios that caused epidemic cholera were of the serogroup O1. The O1 serogroup is classified as two biotypes, classical and El Tor, and is further classified into two major serotypes, Inaba (AC) and Ogawa (AB). In 1993, a new pathogenic serogroup emerged in Bangladesh that was designated O139 Bengal (Silva AJ).

Cholera is asymptomatic in many cases but does cause severe, watery diarrhoea and dehydration in some individuals, which if untreated can rapidly lead to death. Cholera is reported to be endemic in many countries and seven cholera pandemics have been reported globally. The current pandemic is characterized by the predominance of the O1 serogroup of the El Tor biotype, with sporadic emergence of serogroup O139 (WHO).

The two major virulence factors expressed by Vcholerae O1 and O139 are cholera toxin (CT) and the toxin-coregulated pilus (TCP). Cholera toxin is an oligomeric complex made up of six protein subunits: a single copy of the A subunit and five copies of the B subunit.  Subunit B binds to the cell surface via GM1 gangliosides on the surface of target cells. Once bound, the entire toxin complex is endocytosed by the cell and the cholera toxin A1 (CTA1) chain is released by the reduction of a disulfide bridge.  Once inside the cell subunit A activates G protein which then activates adenylate cyclase, eventually leading to enhanced efflux of chloride ions from the intestinal cells, and rapid water loss via the intestine.

References

World Health Organization: Media centre; Cholera

Silva AJ, Benitez JA. (2016). Vibrio cholerae Biofilms and Cholera Pathogenesis. PLoS Negl Trop Dis.Feb 4;10(2):e0004330. PMID: 26845681

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