Vibrio cholerae

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Vibrio cholerae
Cholera bacteria SEM.jpg
Scanning electron microscope image of V. cholerae
Scientific classification Red Pencil Icon.png
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Vibrionales
Family: Vibrionaceae
Genus: Vibrio
Species:
V. cholerae
Binomial name
Vibrio cholerae
Pacini 1854

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 [1] 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 diarrhoea 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, [2] but his discovery was not widely known until Robert Koch, working independently 30 years later, publicized the knowledge and the means of fighting the disease. [3] [4]

Brackish water Water with salinity between freshwater and seawater

Brackish water is water having more salinity than freshwater, but not as much as seawater. It may result from mixing seawater with fresh water together, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak". Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment.

Cholera Bacterial infection of the small intestine

Cholera is an infection of the small intestine by some strains of the bacterium Vibrio cholerae. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and muscle cramps may also occur. Diarrhea can be so severe that it leads within hours to severe dehydration and electrolyte imbalance. This may result in sunken eyes, cold skin, decreased skin elasticity, and wrinkling of the hands and feet. Dehydration can cause the skin to turn bluish. Symptoms start two hours to five days after exposure.

Flagellum part of a cell of some organisms

A flagellum is a lash-like appendage that protrudes from the cell body of certain bacteria and eukaryotic cells termed as flagellates. A flagellate can have one or several flagella. The primary function of a flagellum is that of locomotion, but it also often functions as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. The similar structure in the archaea functions in the same way but is structurally different and has been termed the archaellum.

Contents

Characteristics

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. [1]

Pilus

A pilus is a hair-like appendage found on the surface of many bacteria. The terms pilus and fimbria can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation. All pili in the latter sense are primarily composed of pilin proteins, which are oligomeric.

Pathogenesis

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. [4] In endemic areas, 75% of cases are asymptomatic, 20% are mild to moderate, and 2-5% are severe forms such as cholera gravis. [4] Symptoms include abrupt onset of watery diarrhea (a grey and cloudy liquid), occasional vomiting, and abdominal cramps. [1] [4] 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. [1] 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. [4] [5] [6] 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. [4] [7] 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. [8] [9] In 2002, the WHO deemed that the case fatality ratio for cholera was about 3.95%. [4]

Cholera toxin protein

Cholera toxin is AB5 multimeric protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection. It is a member of the Heat-labile enterotoxin family.

Protein biological molecule consisting of chains of amino acid residues

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity.

Diarrhea Loose or liquid bowel movements

Diarrhea is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin with loss of the normal stretchiness of the skin and irritable behaviour. This can progress to decreased urination, loss of skin color, a fast heart rate, and a decrease in responsiveness as it becomes more severe. Loose but non-watery stools in babies who are exclusively breastfed, however, are normal.

Preventative measures

When visiting areas with epidemic cholera, the following precautions should be observed: drink and use bottled water; frequently wash hands 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. [10] A single dose vaccine is available for those traveling to an area where cholera is common.

Cholera vaccine vaccine that is effective at preventing cholera

Cholera vaccines are vaccines that are effective at preventing cholera. For the first six months after vaccination they provide about 85 percent protection, which decreases to 50 percent or 62 percent during the first year. After two years the level of protection decreases to less than 50 percent. When enough of the population is immunized, it may protect those who have not been immunized.

Genome

V. cholerae has two circular chromosomes, together totalling 4 million base pairs of DNA sequence and 3,885 predicted genes. [11] The genes for cholera toxin are carried by CTXphi (CTXφ), a temperate bacteriophage 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.[ citation needed ] The genes for toxin coregulated pilus are coded by the Vibrio pathogenicity island (VPI). The entire genome of the virulent strain V. cholerae El Tor N16961 has been sequenced, [1] and contains two circular chromosomes. [4] Chromosome 1 has 2,961,149 base pairs with 2,770 open reading frames (ORF's) and chromosome 2 has 1,072,315 base pairs, 1,115 ORF's. The larger first chromosome contains the crucial genes for toxicity, regulation of toxicity, and important cellular functions, such as transcription and translation. [1]

DNA Molecule that encodes the genetic instructions used in the development and functioning of all known organisms and many viruses

Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids; alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life.

In virology, temperate refers to the ability of some bacteriophages to display a lysogenic life cycle. Many temperate phages can integrate their genomes into their host bacterium's chromosome, together becoming a lysogen as the phage genome becomes a prophage. A temperate phage is also able to undergo a productive, typically lytic life cycle, where the prophage is expressed, replicates the phage genome, and produces phage progeny, which then leave the bacterium. With phage the term virulent is often used as an antonym to temperate, but more strictly a virulent phage is one that has lost its ability to display lysogeny through mutation rather than a phage lineage with no genetic potential to ever display lysogeny.

Bacteriophage virus that infects and replicates within bacteria

A bacteriophage, also known informally as a phage, is a virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν (phagein), "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm. Bacteriophages are among the most common and diverse entities in the biosphere. Bacteriophages are ubiquitous viruses, found wherever bacteria exist. It is estimated there are more than 1031 bacteriophages on the planet, more than every other organism on Earth, including bacteria, combined.

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. [4] However, the second chromosome may have once been a megaplasmid because it contains some genes usually found on plasmids. [1]

Plasmid small DNA molecule within a cell that is physically separated from a chromosomal DNA and can replicate independently

A plasmid is a small DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; however, plasmids are sometimes present in archaea and eukaryotic organisms. In nature, plasmids often carry genes that benefit the survival of the organism, such as by providing antibiotic resistance. While the chromosomes are big and contain all the essential genetic information for living under normal conditions, plasmids usually are very small and contain only additional genes that may be useful in certain situations or conditions. Artificial plasmids are widely used as vectors in molecular cloning, serving to drive the replication of recombinant DNA sequences within host organisms. In the laboratory, plasmids may be introduced into a cell via transformation.

MT-RNR2 human gene

Mitochondrially encoded 16S RNA is a mitochondrial ribosomal RNA (rRNA) that in humans is encoded by the MT-RNR2 gene. The MT-RNR2 gene also encodes the Humanin polypeptide that has been the target of Alzheimer's disease research.

A replicon is a DNA molecule or RNA molecule, or a region of DNA or RNA, that replicates from a single origin of replication.

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.

Bacteriophage CTXφ

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. Phage particles are secreted from bacterial cells without lysis. 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 to the ctxA and ctxB 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. [12]

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. [13]

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. [14]

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. V. cholerae thrives in a aquatic environment, particularly in surface water. The primary connection between humans and pathogenic strains is through water, particularly in economically reduced areas that do not have good water purification systems. [9]

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. [15]

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 identified in Bangladesh in 1992 – is confined to Southeast 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.

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 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. [16] Recently, new variant strains have been detected in several parts of Asia and Africa. Observations suggest these strains cause more severe cholera with higher case fatality rates.

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). [17] Natural genetic transformation is a sexual process involving DNA transfer from one bacterial cell to another through the intervening medium, and the integration of the donor sequence into the recipient genome by homologous recombination. Transformation competence in V. cholerae is stimulated by increasing cell density accompanied by nutrient limitation, a decline in growth rate, or stress. [17] The V. cholerae uptake machinery involves a competence-induced pilus, and a conserved DNA binding protein that acts as a ratchet to reel DNA into the cytoplasm. [18] [19]

See also

Related Research Articles

El Tor is a particular strain of the bacterium Vibrio cholerae, the causative agent of cholera. Also known as V. cholera biotype eltor, it has been the dominant strain in the seventh global cholera pandemic. It is distinguished from the classic strain at a genetic level, although both are in the serogroup O1 and both contain Inaba, Ogawa and Hikojima serotypes. It is also distinguished from classic biotypes by the production of hemolysins.

<i>Vibrio</i> genus of bacteria

Vibrio is a genus of Gram-negative bacteria, possessing a curved-rod shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Typically found in salt water, Vibrio species are facultative anaerobes that test positive for oxidase and do not form spores. All members of the genus are motile and have polar flagella with sheaths. Vibrio species typically possess two chromosomes, which is unusual for bacteria. Each chromosome has a distinct and independent origin of replication, and are conserved together over time in the genus. Recent phylogenies have been constructed based on a suite of genes.

Pathogenicity islands (PAIs), as termed in 1990, are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. Pathogenicity islands are found in both animal and plant pathogens. Additionally, PAIs are found in both gram-positive and gram-negative bacteria. They are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon. Therefore, PAIs contribute to microorganisms' ability to evolve.

<i>Vibrio parahaemolyticus</i> species of bacterium

Vibrio parahaemolyticus is a curved, rod-shaped, Gram-negative bacterium found in brackish, saltwater, which, when ingested, causes gastrointestinal illness in humans. V. parahaemolyticus is oxidase positive, facultatively aerobic, and does not form spores. Like other members of the genus Vibrio, this species is motile, with a single, polar flagellum.

Lysogenic cycle

Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and at later events can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood.

Virulence factors are molecules produced by bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to achieve the following:

The RTX toxin superfamily is a group of cytolysins and cytotoxins produced by bacteria. There are over 1000 known members with a variety of functions. The RTX family is defined by two common features: characteristic repeats in the toxin protein sequences, and extracellular secretion by the type I secretion systems (T1SS). The name RTX refers to the glycine and aspartate-rich repeats located at the C-terminus of the toxin proteins, which facilitate export by a dedicated T1SS encoded within the rtx operon.

Shah M. Faruque medical researcher

Shah Mohammad Faruque is a professor in the School of Life Sciences at Independent University Bangladesh (IUB). He is widely recognized for his research in Vibrio cholerae, the bacterium which causes the epidemic diarrhoeal disease Cholera. Among other positions, previously he was a professor at BRAC University; director of the Genomics Centre at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), and formerly director of the Centre for Food and Water Borne Diseases in ICDDR,B. His areas of interest include microbial genomics, bacteriophages, environmental microbiology, ecology, and evolution of bacterial pathogens, particularly those associated with waterborne and foodborne diseases. Faruque is well known for his work on molecular genetics, epidemiology and ecology of the cholera pathogen, and its bacteriophages.

Heat-labile enterotoxin family

In molecular biology, the heat-labile enterotoxin family includes Escherichia coli heat-labile enterotoxin (Elt) and cholera toxin (Ctx) secreted by Vibrio cholerae.

SaPIs are a family of mobile genetic elements resident in the genome of some strains of Staphylococcus aureus. Much like bacteriophages, SaPIs can be transferred to uninfected cells and integrate into the host chromosome. Unlike the bacterial viruses, however, integrated SaPIs are mobilized by host infection with "helper" bacteriophages.

The CTXφ bacteriophage is a filamentous bacteriophage that contains the genetic material needed by the Vibrio cholerae bacterium for the production of cholera toxin, or CT. CTXφ is a positive virus with single-stranded DNA (ssDNA).

Vibrio campbellii is a Gram-negative, curved rod-shaped, marine bacterium closely related to its sister species, Vibrio harveyi. It is an emerging pathogen in aquatic organisms.

In molecular biology, Vibrio cholerae ToxT activated RNAs are small RNAs which are produced by the bacterium Vibrio cholerae. They are regulated by the transcriptional activator ToxT and may play a role in V. cholerae virulence. Two ToxT activated RNAs have been described: TarA and TarB.

The type VI secretion system (T6SS) is molecular machine used by a wide range of Gram-negative bacterial species to transport proteins from the interior of a bacterial cell across the cellular envelope into an adjacent target cell. While often reported that the T6SS was discovered in 2006 by researchers studying the causative agent of cholera, Vibrio cholerae, the first study demonstrating that T6SS genes encode a protein export apparatus was actually published in 2004, in a study of protein secretion by the fish pathogen Edwardsiella tarda.

Blautia obeum is a species of anaerobic, gram-positive bacteria found in the gut.

VqmR sRNA

VqmR small RNA was discovered in Vibrio cholerae, a bacterium which can cause cholera, using differential RNA sequencing (sRNA-seq) under conditions of low and high cell density which were being used to study quorum sensing (QS). QS controls virulence and biofilm formation in Vibrio cholerae; it has been shown previously that it is directed by the Qrr sRNAs. VqmR has been shown to repress the expression of multiple mRNAs including the rtx toxin genes and the vpsT, which is required for biofilm formation. In fact, VqmR which is highly conserved in vibrionaceae, was shown to strongly inhibit biofilm formation by repressing the vpsT gene; it could be the link between biofilm formation and QS.

Contact-dependent growth inhibition (CDI) is a phenomenon where a bacterial cell may deliver a polymorphic toxin molecule into neighbouring bacterial cells upon direct cell-cell contact, causing growth arrest or cell death.

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