title: Genetic and physical evidence for plasmid control of Shigella sonnei form I cell surface antigen.
abstract: Virulent Shigella sonnei synthesize a surface antigen (form I) which appears to be one of several requirements needed for this host to invade epithelial cells. Upon restreaking on agar media, form I cells readily and irreversibly generate form II cells that lack the form I antigen. All form II cells are avirulent. Plasmid deoxyribonucleic acid of form I and II cells of four different S. sonnei isolates, obtained from different areas of the world, was analyzed by agarose gel electrophoresis. A large plasmid (approximately 120 megadaltons in three of the strains) that is present in form I cells was always absent from form II derivatives. Attempts to transfer conjugally only this large plasmid from form I to genetically marked form II cells were unsuccessful. However, a composite molecule, apparently formed by recombination between the large form I plasmid and a self-transmissible plasmid, was found to transfer the form I trait. Transconjugant S. sonnei strains acquiring the form I antigen could retransfer this trait to S. sonnei, Shigella flexneri, or Salmonella typhi. These preliminary findings demonstrate that S. sonnei form I antigen synthesis is mediated by a large plasmid which is lost spontaneously at a relatively high frequency from S. sonnei strains.
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics*; D000954:Antigens, Surface / Q000235:genetics*; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000032:analysis; D010957:Plasmids; D011995:Recombination, Genetic; D012764:Shigella sonnei / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D004251:DNA Transposable Elements; D004269:DNA, Bacterial