Vibrio cholerae

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iVibrio cholerae

TEM image

Scientific classification

Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Gamma Proteobacteria
Order:	Vibrionales
Family:	Vibrionaceae
Genus:	Vibrio
Species:	V. cholerae

Binomial name

Vibrio cholerae
Pacini 1854

Vibrio Cholerae is a gram negative bacterium with a curved-rod shape that causes cholera in humans. It and other species of the genus Vibrio belong to the gamma subdivision of the Proteobacteria. There are two major strains of V. cholerae, classic and El Tor, and numerous other serogroups.

V. cholerae occurs naturally in the plankton of fresh, brackish, and salt water, attached primarily to copepods in the zooplankton. Coastal cholera outbreaks typically follow zooplankton blooms. This makes cholera a typical zoonosis.

V. cholerae colonizes the gastrointestinal tract, where it adheres to villous absorptive cells via pili, and secretes a Binary toxin, called cholera toxin (CT). The two CT subunits are named A and B, and are synthesised in a 1:5 ratio. B subunits bind and internalize A subunits, which are processed to A1. The A1 form catalyses ADP ribosylation from NAD to the regulatory component of adenylate cyclase, thereby activating it. Increased adenylate cyclase activity increases cyclic AMP (cAMP) synthesis causing massive fluid and electrolyte efflux, resulting in diarrhea.

CT is encoded by the ctxAB genes on a specific filamentous bacteriophage. Transduction of this phage is dependent upon bacterial expression of the Toxin Coregulated Pilus (TCP), which is encoded by the V. cholerae pathogenicity island (VPI). VPI is generally only present in virulent strains and is laterally transferred. VPI was originally thought to encode a filamentous phage responsible for transfer. This theory was discredited by a study of 46 diverse V. cholerae isolates which found no evidence of VPI phage production. The generalized transduction phage CP-T1 has been shown to transduce the entire VPI which is then integrated at the same chromosomal location. Also, VPI has been shown to excise and circularize to produce pVPI via a specialised mechanism involving VPI-encoded recombinases. It is not known whether pVPI is involved in CP-T1 transduction or if it is perhaps a component of an alternative VPI mobilization mechanism.

The bacterium was first isolated as the cause of cholera by Italian anatomist Filippo Pacini in 1854, but his discovery was not widely known until Robert Koch, working independently thirty years later, publicized the knowledge and the means of fighting the disease.