| Background Vibrio cholerae is the causative agent of cholerae, an acute dehydrating diarrhea that occurs in epidemic and pandemic forms. Seven distinct pandemics of cholerae have occurred since the onset of the first pandemic in 1817. The species V. cholerae is classified on the basis of its somatic antigens (O-antigens) into groups, and there are at least 206 known serogroups of V. cholerae. Only serogroup Ol was supposed to include all strains of cholerae responsible for epidemic of cholerae until the emergences of serogroup O139 in 1992. Extensive outbreaks have occurred in various regions of the world (including Xinjiang province in China in 1993). Epidemics of cholera caused by this new serogroup continue to occur, apparently representing the beginning of the eighth cholera pandemic. Since the initial emergence of Vibrio cholerae, new variants of the pathogen with altered genetic and phenotypic characteristics have appeared frequently. So the genetics and the evolution of Vobrio cholerae O139 attract worldwide attention. Vobrio cholerae O139 was the only non-Ol V. cholerae capable of causing epidemic outbreaks. Immediately after the emergence of the VC O139 comparative analyses of V. cholerae O139 strains were carried toinvestigate the origin of this new serogroup.The emergence of the O139 clone with pandemic potential stimulated increased interest in the molecular basis of pathogenesis in V. cholerae and the degree to which genes determining serotype and virulence properties are subject to horizontal transfer and recombination among strains.Molecular analysis indicated that O139 strains were closely related to Ol El Tor biotype strains. O139 strains had all the same virulence factors normally found in Ol El Tor strains. The initial O139 strain may have emerged from serotype-specific genetic change in an ancestral El Tor strain. But O139 strains are encapsulated and its antigen includes an O-antigen capsue and bacterial lip polysaccharide, which are different from Ol El Tor strains. The gene cluster responsible for O-antigen biosynthesis of 0139 serogroup of V. cholerae has been found to be closely related to the of O22 serogroup. Many studies suggested that V. cholerae O139 was derived from a seventh-pandemic El Tor clone by horizontal gene transfer.The principal virulence factor of V. cholerae is cholera toxin (CT), a potent, A-B-type exotoxin that ADP-ribosylates proteins within intoxicated intestinal epithelial cells. The CT produced by V. cholerae during the organism's colonization of its host's small intestine accounts for a majority of the symptoms that characterize the disease process. The genes encoding CT (the operon ctxAE] are not integral components of the V. cholerae genome, but instead are elements of the genome of a filamentous bacteriophage, The genome of CTXO, a 6.9 kb single-stranded DNA filamentous bacteriophage. CTXO genome encodes a site-specific recombination system that catalyzes the integration of the phage DNA into the attRS site on the El Tor V. cholerae chromosome to form lysogens. CTXO is transmissible, the bacterial receptor for CTXO, the toxin-coregulated pilus, is encoded by an operon (top) that is part of a transmissible pathogenicity island.Strategies for the prevention and control of an infectious disease like cholera depend on understanding the origin, transmission, and other characteristics associated with the epidemic and its spread. Although substantial information is available on the study of the origin of V. cholerae O139, its origin is not clear now. Factors affected the emergence of V.cholerae O139 also remain an enigma.In 1993, there was an outbreak of cholera caused by serogroup O139 in Xinjiang province. Since the outbreak of V. cholerae O139 in Xinjiang China, it hasn't resulted in epidemic, but the involved areas have been increasing and the number of sporadic case hasn't been obviously controlled. To study its origin and its characteristics, we select three strains of Vibrio cholerae as our subject strain. One is serogroup O139 isola...
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