title: Virulence-associated chromosomal loci of Shigella flexneri identified by random Tn5 insertion mutagenesis.
abstract: Shigellae are the causative agents of bacillary dysentery and are capable of invading epithelial cells, multiplying therein and spreading into adjacent cells. To identify genes on the chromosome associated with the virulence phenotype, 9114 independent Tn5 insertion mutants were isolated in a virulent strain of Shigella flexneri. By using an in vitro assay for intercellular spread or an animal infection model, the Serény test, 50 chromosomal Tn5 mutants with reduced virulence were identified. The 50 mutants were characterized with respect to their virulence phenotypes, including three different mutations that affect invasion of epithelial cells, bacterial metabolism and structure of lipopolysaccharide. Mutants with reduced invasive ability were further characterized and it was found that two of them had decreased levels of IpaB, C and D antigens as well as the mRNA for the ipaBCD operon encoded by the large virulence plasmid, suggesting that positive regulatory elements for the ipaBCD operon are encoded by the chromosome. Assignment of the 50 Tn5 insertions of the mutants to the 19 NotI restriction fragments of the chromosomal DNA has permitted the identification of at least nine virulence-associated chromosomal loci.
authors.affiliation: Department of Bacteriology, University of Tokyo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Okada
authors.forename: C
authors.initials: C
authors.lastname: Sasakawa
authors.forename: T
authors.initials: T
authors.lastname: Tobe
authors.forename: M
authors.initials: M
authors.lastname: Yamada
authors.forename: S
authors.initials: S
authors.lastname: Nagai
authors.forename: K A
authors.initials: KA
authors.lastname: Talukder
authors.forename: K
authors.initials: K
authors.lastname: Komatsu
authors.forename: S
authors.initials: S
authors.lastname: Kanegasaki
authors.forename: M
authors.initials: M
authors.lastname: Yoshikawa
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000096:biosynthesis; D015153:Blotting, Western; D002478:Cells, Cultured; D002876:Chromosomes, Bacterial / Q000648:ultrastructure; D004251:DNA Transposable Elements; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D007700:Kinetics; D008070:Lipopolysaccharides / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009876:Operon; D010641:Phenotype; D010957:Plasmids; D011897:Random Allocation; D012763:Shigella flexneri / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D000942:Antigens, Bacterial; D004251:DNA Transposable Elements; D008070:Lipopolysaccharides; D015252:Deoxyribonucleases, Type II Site-Specific; C038565:GCGGCCGC-specific type II deoxyribonucleases