Random Selection of Micro-Organism ; 6 Vibrio Cholerae : A Comma Shape Bacteria
1) Vibrio cholerae :
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. The bacterium's natural habitat is brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and other shellfish.
Some strains of V. cholerae cause the disease cholera, which can be derived from the consumption of undercooked or raw marine life species. 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 in 1854 by Italian anatomist Filippo Pacini and by the Catalan Joaquim Balcells i Pascual in the same year,
but their discovery was not widely known until Robert Koch, working independently 30 years later, publicized the knowledge and the means of fighting the disease.
Classifications :
Kingdom : Bacteria
Phylum : Proteobacteria
Class : Gammaproteobacteria
Order : Vibrionales
Family : Vibrionaceae
Genus : Vibrio
Introduction :
Vibrio cholerae is a "comma" shaped Gram-negative bacteria with a single, polar flagellum for movement. There are numerous strains of V. cholerae, some of which are pathogenic and some of which are not.
The most wide sweeping pathogenic strain is the Vibrio cholerae serotype O1 El Tor N16961 strain that causes the pandemic disease cholera. The latest pathogenic serotype O139 was discovered in 1992.
The El Tor strain was active in the seventh and most recent pandemic of cholera from 1960's-1970's, as well as in the early 1990's along with serotype O139, both displaying resistance to multiple drugs.
The bacteria infects the intestine and increases mucous production causing diarrhea and vomiting which result in extreme dehydration and, if not treated, death. It is usually transmitted through the feces of an infected person, often by way of unclean drinking water or contaminated food.
Since water treatment and sanitation is more advanced in the United States, cholera is not nearly as high of a public health threat in the US as it is in densely populated, economically reduced areas like India or sub-Saharan Africa where water and sewage treatment technology is low.
It is for this great risk to human health that makes it so worthy of studying and sequencing. And because of the variety of strains, it could be possible to determine the pathogenicity of new strains by comparing their genomes to strains of known pathogenic status.
Characteristics :
V. cholerae is a highly motile, comma shaped, halophilic, gram-negative rod. 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. The Vibrios tolerate alkaline media that kill most intestinal commensals, but they are sensitive to acid.
V. cholerae is a facultative anaerobe, and can undergo respiratory and fermentative metabolism.
It measures 0.3 micron in diameter and 1.3 micron in length with average swimming velocity of around 75.4 +/- 9.4 microns/sec.[8]
Ecology :
V. cholerae thrives in a water ecology, particularly surface water.
The primary connection between humans and pathogenic strains is through water, particularly in economically reduced areas that don't have good water purification systems.
Non-pathogenic strains are also present in water ecologies.
It is thought that it is the wide variety of strains of pathogenic and non-pathogenic strains that co-exist in aquatic enviornments that 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.
Pathogenicity :
Pathology :
V. cholerae enters the human body through injestion of contaminated food or water. The bacteria enters the instestine, imbeds itself in the villi of absorptive intestinal cells, and releases cholera toxin.
Cholera toxin (CT) is an enterotoxin made up of five B-subunits that form a pore to fits one A-subunit.
CT is made from filamentous phage gene, CTXφ. A phage gene is also responsible for another virulence factor of V. cholerae, which is toxin co-regulated pilus (TCP), which acts as a receptor for CTXφ.
Physiological responses and symptoms that follow release of cholera toxin include stimulation of the mucosal lining of the intestine to secrete fluids.
This causes vomiting and watery diarhea that has a "rice water" quality. Death can occur from extreme dehydration and if not treated does occur 50-70% of the time.
Treatment includes rehydration and rplacement of lost electrolytes, which are important ions, such as sodium and potassium, used in biochemical processes to keep the body alive.
Because of the low quality of water treatment in many poverty ridden countries, rehydration with clean water can be impossible without medical aid and supplies.
Antibiotic Resistance :
Cell Structure & Metabolism :
V. cholerae is Gram-negative has what is called a comma shaped cell body and contains a singular polar flagellum used for motility.
V. cholerae serogroup O1 does not have a polysaccharide capsule, but serogroup O139 does contain a polysaccaride capsule made up of "N-acetylglucosamine, N-acetylquinovosamine (QuiNAc), galacturonic acid (GalA), and galactose and two residues of 3,6-dideoxyxylohexose (Xylhex)."
When V. cholerae are growing during the logarithmic phase there is little or no change to the cellular envelope.
However, towards the end of logarithmic phase and into the begining of stationary phase cholera toxin is produced, which is accompanied by internal swelling of the cell and permeability changes to the cellular envelope.
Anaerobic respiration appears to be the energy producing process for V. cholerae since the ileum, which is the final portion of the small intestine before entering the colon, is an anaerobic environment.
"Alternative electron acceptors such as fumarate, or donors such as formate or glycerol-3-phosphate" are possible players in the metabolism process.
Genome :
V. cholerae has two circular chromosomes, together totalling 4 million base pairs of DNA sequence and 3,885 predicted genes.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. 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, and contains two circular chromosomes.
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.
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 & 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.
Treatments :
Preventive 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.
Supplying proper, safe water is important. A precaution to take is to properly sanitize.
Hand hygiene is an essential in areas where soap and water is not available. When there is no sanitation available for hand washing, scrub hands with ash or sand and rinse with clean water.
A single dose vaccine is available for those traveling to an area where cholera is common.
There is a V. cholerae vaccine available to prevent disease spread. The vaccine is known as the, "oral cholera vaccine" (OCV). There are three types of OCV available for prevention : Dukoral®, Shanchol™, and Euvichol-Plus®.
All three OCVs require two doses to be fully effective. Countries who are endemic or have an epidemic status are eligible to receive the vaccine based on several criteria :
Risk of cholera, Severity of cholera, WASH conditions and capacity to improve, Healthcare conditions and capacity to improve, Capacity to implement OCV campaigns, Capacity to conduct M&E activities, Commitment at national and local level.
Since May the start of the OCV program to May 2018 over 25 million vaccines have been distributed to countries who meet the above criteria.
Really appreaciate their works and the awareness they are spreafding to the peoples
#cholera
Courtessy :globalhealth.org
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