title: Role of IS1 in the conversion of virulence (Vi) antigen expression in Enterobacteriaceae.
abstract: When Escherichia coli HB101 harbors pWR127, a plasmid comprising the viaB gene from Citrobacter freundii WR7004 and the ColE1-derived pACKC1, the strain produces the virulence (Vi) antigen. Vi antigen expression is abolished (Vi- phenotype), however, when an IS1 or IS1-like DNA element inserts into the viaB region. To determine the sites of IS1 insertion, pWR127 DNAs extracted from 95 independently isolated Vi- strains were analyzed by digestion with the restriction endonuclease PstI and agarose gel electrophoresis. Ten insertion sites were found distributed non-randomly in an area of about 1.3 kb. Nine Vi+ strains (two Citrobacter, two E. coli, and five Salmonella strains), four of which contain pWR127, were then tested for the presence of IS1 by DNA-DNA hybridization. Of the nine strains, five were stable Vi+ and did not contain IS1. The other four which generated Vi- strains, contained IS1. When pRR134, a plasmid that contains IS1 was transferred into a stable Vi+ Salmonella typhimurium strain carrying pWR127 (OU5140), Vi- strains were produced from which pWR127 derivatives carrying IS1 inserts could be isolated. It appears, therefore, that the presence of an IS1 or IS1-like element in a strain is required for conversion of the Vi+ expression state to the Vi- expression state.
authors.affiliation: Department of Microbiology and Immunology, Chang Gung Medical College, Taoyuan, Taiwan.
authors.forename: J T
authors.initials: JT
authors.lastname: Ou
authors.forename: C J
authors.initials: CJ
authors.lastname: Huang
authors.forename: H S
authors.initials: HS
authors.lastname: Houng
authors.forename: L S
authors.initials: LS
authors.lastname: Baron
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics*; D004251:DNA Transposable Elements / Q000235:genetics*; D004755:Enterobacteriaceae / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D009693:Nucleic Acid Hybridization; D010957:Plasmids / Q000235:genetics; D011135:Polysaccharides, Bacterial; D014774:Virulence / Q000235:genetics*
chemical_list: D000942:Antigens, Bacterial; D004251:DNA Transposable Elements; D011135:Polysaccharides, Bacterial