[Phenomenology and molecular mechanisms of Shigella sonnei dissociation: its variability in model in vivo and in vitro systems].

The dynamics of the accumulation of phase II S. sonnei in the infectious process in germ-free rats, during cultivation and in subcultures was studied. The in vivo variability of S. sonnei showed a sharply defined phasic character of the process with the periods of the apparent absence of phase II, the increase of its occurrence and stabilization with the preservation of S-forms in minor amounts. Kanamycin-resistant phase II accumulated in vivo more rapidly than in vitro. Cultivation with sodium desoxycholate was found to accelerate the process of disassociation. The characteristic feature of all dissociants detected in all systems was their plasmid profile: in phase I, plasmids of 120 and 60 Md, as well as small plasmids, were detected; in phase II disassociants, plasmid with a molecular weight of 120 Md was absent. The restriction analysis of total plasmid DNA by means of restrictase EcoR1 showed the absence of 3 fragments in phase II while other 13 fragments were retained. These results open prospects for the molecular cloning of the gene antigen of phase II.