Cholera causes: Difference between revisions
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{{CMG}}; '''Associate Editors-In-Chief:''' [[Priyamvada Singh|Priyamvada Singh, MBBS]] [mailto:psingh13579@gmail.com] | {{CMG}}; '''Associate Editors-In-Chief:''' [[Priyamvada Singh|Priyamvada Singh, MBBS]] [mailto:psingh13579@gmail.com] | ||
==Overview== | ==Overview== | ||
'''''Vibrio cholerae''''' is a [[gram negative]] [[bacterium]] with a curved-rod shape that causes [[cholera]] in [[human]]s.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 }}</ref> ''V. cholerae'' 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. | '''''Vibrio cholerae''''' is a [[gram negative]] [[bacterium]] with a curved-rod shape that causes [[cholera]] in [[human]]s.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 }}</ref> ''V. cholerae'' 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.<ref name=Sherris>{{cite book | author = Ryan KJ, Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | pages = 376–7 |publisher = McGraw Hill | year = 2004 | isbn = 0838585299 }}</ref> | ||
''V. cholerae'' 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. | ''V. cholerae'' 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. | ||
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''V. cholerae'' colonizes the [[gastrointestinal]] tract, where it adheres to [[villi|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]]. | ''V. cholerae'' colonizes the [[gastrointestinal]] tract, where it adheres to [[villi|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]]. | ||
*The major reservoir for cholera was long assumed to be humans, but some evidence suggests that it is the aquatic environment. | |||
**''[[Vibrio cholera]]'' is not dependent on humans for its propagation. | |||
**''[[Vibrio cholera]]'' can grow inbrackish estuaries, coastal seawaters (in close association with copepods or other zooplankton), and water of lower salinity when it is warm and adequate organic material is available.<ref name=Wilcox> Wilcox, Bruce A., and Rita R. Colwell. "Emerging and reemerging infectious diseases: biocomplexity as an interdisciplinary paradigm." EcoHealth 2.4 (2005): 244-257.</r | |||
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. | 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. | ||
Revision as of 11:05, 7 October 2016
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Priyamvada Singh, MBBS [2]
Overview
Vibrio cholerae is a gram negative bacterium with a curved-rod shape that causes cholera in humans.[1] V. cholerae 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.[1]
V. cholerae 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.
Habitat
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.
Pathogenesis
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.
- The major reservoir for cholera was long assumed to be humans, but some evidence suggests that it is the aquatic environment.
- Vibrio cholera is not dependent on humans for its propagation.
- Vibrio cholera can grow inbrackish estuaries, coastal seawaters (in close association with copepods or other zooplankton), and water of lower salinity when it is warm and adequate organic material is available.
Image: Cholera16.jpeg| Typical Vibrio cholera contaminated water supply. From Public Health Image Library (PHIL). [2]
Image: Cholera07.jpeg| Scanning electron micrograph (SEM) depicts a number of Vibrio parahaemolyticus bacteria; Mag. 19058x. From Public Health Image Library (PHIL). [2] Image: Cholera06.jpeg| Scanning electron micrograph (SEM) depicts a grouping of Vibrio vulnificus bacteria; Mag. 13184x. From Public Health Image Library (PHIL). [2] Image: Cholera05.jpeg| Scanning electron micrograph (SEM) depicts a flagellated Vibrio vulnificus bacterium; Mag. 26367x. From Public Health Image Library (PHIL). [2] Image: Cholera04.jpeg| Scanning electron micrograph (SEM) depicts a grouping of Vibrio vulnificus bacteria; Mag. 13184x. From Public Health Image Library (PHIL). [2] Image: Cholera03.jpeg| Scanning electron micrograph (SEM) depicts a number of Vibrio cholerae bacteria of the serogroup 01; Magnified 22371x. From Public Health Image Library (PHIL). [2]
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