is a Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
, comma-shaped bacterium. Some strains of V. cholerae
cause the disease cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
. V. cholerae
is facultatively anaerobic
Anaerobic is a word which literally means without oxygen, as opposed to aerobic.In wastewater treatment the absence of oxygen is indicated as anoxic; and anaerobic is used to indicate the absence of a common electron acceptor such as nitrate, sulfate or oxygen.Anaerobic may refer to:*Anaerobic...
and has a flagella at one cell pole. V. cholerae
was first isolated as the cause of cholera by Italian anatomist Filippo Pacini
Filippo Pacini was an Italian anatomist, posthumously famous for isolating the cholera bacillus Vibrio cholerae in 1854, well before Robert Koch's more widely accepted discoveries thirty years later....
in 1854, but his discovery was not widely known until Robert Koch
Heinrich Hermann Robert Koch was a German physician. He became famous for isolating Bacillus anthracis , the Tuberculosis bacillus and the Vibrio cholerae and for his development of Koch's postulates....
, working independently thirty years later, publicized the knowledge and the means of fighting the disease.
V. cholerae pathogenicity
Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism.It is often used interchangeably with the term "virulence", although virulence is used more specifically to describe the relative degree of damage done by a pathogen, or the degree of pathogenicity caused by...
genes code for proteins directly or indirectly involved in the virulence of the bacteria. During infection, V. cholerae
secretes cholera toxin
Cholera toxin is a protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection.- Structure :...
, a protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that causes profuse watery diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
. Colonization of the small intestine also requires the toxin coregulated pilus
right|thumb|350px|Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, brings the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell...
(TCP), a thin, flexible, filamentous, appendage on the surface of bacterial cells.
has two circular chromosomes, together totalling 4 million base pairs of DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
sequence and 3,885 predicted genes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
. The genes for cholera toxin are carried by CTXphi, a temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
inserted into the V. cholerae
genome. CTXφ can transmit cholera toxin genes from one V. cholerae
strain to another, one form of horizontal gene transfer
Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...
. The genes for toxin coregulated pilus are coded by the VPI pathogenicity island
Pathogenicity islands are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. They are incorporated in the genome of pathogenic organisms but are usually absent from those non-pathogenic organisms of the same or closely related species...
CTXφ (also called CTXphi) is a filamentous phage
A filamentous phage is a type of bacteriophage shaped like a rod filament. Filamentous phages usually contain a genome of single-stranded DNA and infect Gram-negative bacteria.-Types of filamentous phage:*Ff phages - these infect E...
that contains the genes for cholera toxin. Infectious CTXφ particles are produced when V. cholerae
infect humans. Phage particles are secreted from bacterial cells without lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....
. When CTXφ infects V. cholerae
cells, it integrates into specific sites on either chromosome. These sites often contain tandem arrays of integrated CTXφ prophage. In addition the the ctxA
genes encoding cholera toxin, CTXφ contains eight genes involved in phage reproduction, packaging, secretion, integration, and regulation. The CTXφ genome is 6.9 kb long.
VPI pathogenicity island
The VPI pathogenicity island contains genes involved in the creation of toxin coregulated pilus (TCP). It is a large genetic element (~40 kb) flanked by two repetitive regions (att
-like sites), resembling a transposon
Transposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
in structure. The VPI pathogenicity island is composed of two gene clusters: the TCP cluster and the ACF cluster. Among the genes of the VPI pathogenicity island, twenty genes have been identified, where some genes are outside of the clusters like tagA
. The acf
cluster is composed of 4 genes: acfABC
, encoding a putative accessory colonization factor activated by toxR. 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. Recent studies indicate that global warming creates a favourable environment for the bacteria.
Cholera infections are most commonly acquired from drinking water in which V. cholerae
is found naturally or into which it has been introduced from the feces of an infected person. Other common vehicles include contaminated fish and shellfish, produce, or leftover cooked grains that have not been properly reheated. Transmission from person to person, even to health care workers during epidemics, is rarely documented.
Diversity and evolution
Serotype or serovar refers to distinct variations within a subspecies of bacteria or viruses. These microorganisms, viruses, or cells are classified together based on their cell surface antigens...
of V. cholerae
, O1 and O139, cause outbreaks of cholera. O1 causes the majority of outbreaks, while O139 – first identified in Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
in 1992 – is confined to South-East Asia. Many other serogroups of V. cholerae
, with or without the cholera toxin gene (including the nontoxigenic strains of the O1 and O139 serogroups), can cause a cholera-like illness. Only toxigenic strains of serogroups O1 and O139 have caused widespread epidemics.
O1 has 2 biotypes, classical and El Tor, and each biotype has 2 distinct serotypes, Inaba and Ogawa. The symptoms of infection are indistinguishable, although more people infected with the 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 Bangladesh and India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. Recently, new variant strains have been detected in several parts of Asia and Africa. Observations suggest that these strains cause more severe cholera with higher case fatality rates.