Role of IS1 in the Conversion of Virulence (Vi) Antigen Expression inEnterobacteriaceae

摘要

When Escherichia coli HB101 harbors pWR127, a plasmid comprising the viaB genefrom Citrobacter freundii WR7004 and the ColE1-derived pACKCl, the strain produces the virulence (Vi) antigen. Viantigen expression is abolished (Vi(-) phenotype), however, when an IS/ or IS/-like DNA element inserts into the viaB region. To determine the sites of IS/ 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 IS/ by DNA-DNA hybridization. Of the nine strains, five were stable Vi(-) and did not contain IS/. The other four which generated Vi(-) strains, contained IS/. When pRR134, a plasmid that contains IS/ was transferred into a stable Vi(-) Salmonella typhimurium strain carrying pWR127 (OU5140), Vi(-) strains were produced from which pWR127 derivatives carrying IS/ inserts could be isolated. It appears, therefore, that the presence of an IS/ or IS/-like element in a strain is required for conversion of the Vi(-) expression state to the Vi(-) expression state.