Vibrio cholerae.html |
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| Vibrio cholerae Pacini 1854 |
Vibrio cholerae (also Kommabacillus) is a gram negative curved-rod shaped bacterium with a polar flagellum that causes cholera in humans.12 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.
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.citation needed
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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 villi. Additionally, it produces two different proteases called chitinase and mucinase. Chitinase is responsible for the ability of Vibrio cholerae to enter copepods. Mucinase is a non-specific protease that assists entry into the human gastro-intestinal tract.
Vibrio cholerae produces what is called a ZOT, termed as "Zona Occludans Toxin". This toxin specifically attacks the zona occludans or "tight" junctions joining epithelial cells.
Passage of the bacterium through the gastrointestinal tract is believed to be a major contributor to its enhanced pathogenicity as compared to colonies cultured in vitro. This enhanced virulence affords a competitive advantage in nature, this competitive advantage is lost once virulent bacteria are transferred to in vitro cultures. 3. V. cholerae strains possessing this higher virulence were found to possess an increase in transcription of genes coding for biosynthesis of amino acids, iron uptake systems, ribosomal proteins, and formation of a periplasmic nitrate reductase complex that may allow for respiration under low oxygen tension, all of which enhance proliferation in the rice water stool that is characteristic of cholera infection 4
Genomics and Evolution
The 4.0 Mbp genome of N16961, an O1 serogroup, El Tor biotype, 7th pandemic strain of V. cholerae, is comprised of two circular chromosomes of unequal size that are predicted to encode a total of 3,885 genes. The genomic sequence of this representative strain has furthered our understanding of the genetic and phenotypic diversity found within the species V. cholerae. Sequence data have been used to identify horizontally acquired sequences, dissect complex regulatory and signaling pathways, and develop computational approaches to predict patterns of gene expression and the presence of metabolic pathway components. Microarrays are being used to study the evolution of the organism. Genomic sequencing of additional strains, subtractive hybridization studies and the introduction of new model systems have also contributed to the identification of novel sequences and pathogenic mechanisms associated with other strains.2
See also
References
- ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.), McGraw Hill. ISBN 0838585299.
- ^ a b Faruque SM; Nair GB (editors). (2008). Vibrio cholerae: Genomics and Molecular Biology, Caister Academic Press. ISBN 978-1-904455-33-2 , http://www.horizonpress.com/vib.
- ^ Merrell DS, Butler SM, Qadri F, Dolganov NA, Alam A, Cohen MB, Calderwood SB, Schoolnik GK, Camilli A. Host-induced epidemic spread of the cholera bacterium. Nature. 2002 Jun 6;417(6889):642-5
- ^ Merrell DS, Butler SM, Qadri F, Dolganov NA, Alam A, Cohen MB, Calderwood SB, Schoolnik GK, Camilli A. Host-induced epidemic spread of the cholera bacterium. Nature. 2002 Jun 6;417(6889):642-5