VIBRIO CHOLERAE is a
Gram-negative , comma-shaped bacterium . The
bacterium's natural habitat is brackish or saltwater. Some strains of
V. cholerae cause the disease cholera . V. cholerae is a facultative
anaerobe and has a flagellum at one cell pole as well as pili . V.
cholerae can undergo respiratory and fermentative metabolism. When
ingested, V. cholerae can cause diarrhea and vomiting in a host within
several hours to 2–3 days of ingestion. 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
* 1 Characteristics * 2 Pathogenesis * 3 Preventative measures
* 4 Genome
* 5 Ecology and epidemiology * 6 Diversity and evolution * 7 Natural genetic transformation * 8 Gallery * 9 See also * 10 References * 11 External links
V. cholerae is Gram-negative and comma-shaped. Initial isolates are slightly curved, whereas they can appear as straight rods upon laboratory culturing. The bacterium has a flagellum at one cell pole as well as pili . V. cholerae is a facultative anaerobe , and can undergo respiratory and fermentative metabolism.
V. cholerae pathogenicity genes code for proteins directly or indirectly involved in the virulence of the bacteria. During infection, V. cholerae secretes cholera toxin , a protein that causes profuse, watery diarrhea (known as "rice-water stool"). Colonization of the small intestine also requires the toxin coregulated pilus (TCP), a thin, flexible, filamentous appendage on the surface of bacterial cells. V. cholerae can cause syndromes ranging from asymptomatic to cholera gravis. In endemic areas, 75% of cases are asymptomatic, 20% are mild to moderate, and 2-5% are severe forms such as cholera gravis. Symptoms include abrupt onset of watery diarrhea (a grey and cloudy liquid), occasional vomiting , and abdominal cramps. Dehydration ensues, with symptoms and signs such as thirst, dry mucous membranes, decreased skin turgor, sunken eyes, hypotension , weak or absent radial pulse , tachycardia , tachypnea , hoarse voice, oliguria , cramps, renal failure , seizures , somnolence , coma, and death. Death due to dehydration can occur in a few hours to days in untreated children. The disease is also particularly dangerous for pregnant women and their fetuses during late pregnancy, as it may cause premature labor and fetal death. In cases of cholera gravis involving severe dehydration, up to 60% of patients can die; however, less than 1% of cases treated with rehydration therapy are fatal. The disease typically lasts 4–6 days. Worldwide, diarrhoeal disease , caused by cholera and many other pathogens, is the second-leading cause of death for children under the age of 5 and at least 120,000 deaths are estimated to be caused by cholera each year. In 2002, the WHO deemed that the case fatality ratio for cholera was about 3.95%.
When visiting areas with epidemic cholera, the following precautions should be observed: drink and use bottled water; wash hands often with soap and safe water; use chemical toilets or bury feces if no restroom is available; do not defecate in any body of water and cook food thoroughly.
V. cholerae has two circular chromosomes , together totalling 4
million base pairs of
The second chromosome is determined to be different from a plasmid or megaplasmid due to the inclusion of housekeeping and other essential genes in the genome, including essential genes for metabolism, heat-shock proteins, and 16S rRNA genes, which are ribosomal subunit genes used to track evolutionary relationships between bacteria. Also relevant in determining if the replicon is a chromosome is whether it represents a significant percentage of the genome, and chromosome 2 is 40% by size of the entire genome. And, unlike plasmids, chromosomes are not self-transmissible. However, the second chromosome may have once been a megaplasmid because it contains some genes usually found on plasmids.
V. cholerae contains a genomic island of pathogenicity and is lysogenized with phage DNA. That means that the genes of a virus were integrated into the bacterial genome and made the bacteria pathogenic. The molecular pathway involved in expression of virulence is discussed in the pathology and current research sections below.
CTXφ (also called CTXphi) is a filamentous phage that contains the
genes for cholera toxin . Infectious CTXφ particles are produced when
V. cholerae infects humans.
VIBRIO PATHOGENICITY ISLAND
The Vibrio pathogenicity island (VPI) contains genes primarily involved in the production of toxin coregulated pilus (TCP). It is a large genetic element (about 40 kb) flanked by two repetitive regions (att-like sites), resembling a phage genome in structure. The VPI contains two gene clusters, the TCP cluster, and the ACF cluster, along with several other genes. The acf cluster is composed of four genes: acfABCD. The tcp cluster is composed of 15 genes: tcpABCDEFHIJPQRST and regulatory gene toxT.
ECOLOGY AND EPIDEMIOLOGY
The main reservoirs of V. cholerae are people and aquatic sources such as brackish water and estuaries , often in association with copepods or other zooplankton , shellfish , and aquatic plants.
Nonpathogenic strains are also present in water ecologies. The wide variety of pathogenic and nonpathogenic strains that co-exist in aquatic environments are thought to allow for so many genetic varieties. Gene transfer is fairly common amongst bacteria, and recombination of different V. cholerae genes can lead to new virulent strains.
A symbiotic relationship between V. cholerae and Ruminococcus obeum has been determined. R. obeum autoinducer represses the expression of several V. cholerae virulence factors . This inhibitory mechanism is likely to be present in other gut microbiota species which opens the way to mine the gut microbiota of members in specific communities which may utilize autoinducers or other mechanisms in order to restrict colonization by V.cholerae or other enteropathogens .
DIVERSITY AND EVOLUTION
Two serogroups of V. cholerae, O1 and O139, cause outbreaks of
cholera. O1 causes the majority of outbreaks, while O139 – first
V. cholerae O1 has two biotypes, classical and
El Tor , and each
biotype has two distinct serotypes, Inaba and Ogawa. The symptoms of
infection are indistinguishable, although more people infected with
El Tor biotype remain asymptomatic or have only a mild illness. In
recent years, infections with the classical biotype of V. cholerae O1
have become rare and are limited to parts of
NATURAL GENETIC TRANSFORMATION
V. cholerae can be induced to become competent for natural genetic
transformation when grown on chitin , a biopolymer that is abundant in
aquatic habitats (e.g. from crustacean exoskeletons). Natural genetic
transformation is a sexual process involving
Vibrio cholerae bacteria *
Diagram of the bacterium, V. cholerae *
Microscope slide with a sample of "colera asiaticus", prepared by Pacini in 1854
* Molecular and Cellular Biology portal
* ^ A B C D E F G "Laboratory Methods for the Diagnosis of Vibrio cholerae" (PDF). Centre for Disease Control. Retrieved 29 October 2013.
* ^ See:
* Filippo Pacini (1854) "Osservazioni microscopiche e deduzioni patologiche sul cholera asiatico" (Microscopic observations and pathological deductions on Asiatic cholera), Gazzetta by tiadwe Medica Italiana: Toscana, 2nd series, 4 (50) : 397-401 ; 4 (51) : 405-412. The term "vibrio cholera" appears on page 411. * Reprinted (more legibly) as a pamphlet.
* ^ Bentivoglio, M; Pacini, P (1995). "Filippo Pacini: A
determined observer". Brain Research Bulletin. 38 (2): 161–5. PMID
7583342 . doi :10.1016/0361-9230(95)00083-Q .
* ^ A B C D E F G H I Howard-Jones, N (1984). "
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