Vibrio cholerae O1 biovar ElTor str. N16961.
This is an epidemic serogroup of Vibrio cholerae isolated in 1971 in Bangladesh and is distinguished from the classical biotype due to hemolysin production. It contains 2 chromosomes. The first, and larger chromosome, contains many essential cell functions, as well as virulence genes contained within pathogenicity islands (PAIs). One major pathogenicity determinant is encoded within a PAI that is contained inside an integrated phage (CTXphi) on chromosome 1 that codes for the cholera toxin, an adenylate cyclase. Once the toxin is injected into host cells, it results in secretion of chlorine ions, which leads to increased water secretion, dehydration, and eventually, death. Up to 20 litres of water a day may be lost. The second chromosome also has important cell functions, but has a preponderance of genes associated with energy and transport functions, including signal transduction systems, and in addition, DNA repair enzymes. Chromosome 2 also has the integron island, a large variable region of the chromosome that functions as a gene capture system, some of which are associated with antibiotic resistance. There are 105 genes that have copies on both chromosomes.
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