[Interaction of Shigella sonnei phase-I strains carrying F'- or R386 plasmids with continuous HeLa- and L-line cells].

The region of S. sonnei chromosome, located to the left of the gene lac I, has been found to be linked with the capacity of these bacteria for penetrating epithelial cells: this capacity is sharply suppressed in transconjugates carrying plasmids F' which cover the above-mentioned chromosomal region in recipients. The loss of virulence by transconjugates with transferred plasmids F'lac is not linked with the transfer of F factor proper, as those transconjugates which have acquired plasmids F' from E.

[Separation of Shigella toxins into fractions differing in biological activity and characteristics of the fractions inducing penetration in avirulent strains].

The results obtained in the study of the biological activity of the lysates of 14 Sh. flexneri and Sh. sonnei strains differing in their virulence are presented.

[Effect of mutations imparting resistance to antibiotics having different mechanisms of action on the virulence of Shigella flexneri].

The study of the interaction between mutants of Sh. flexneri 2a and epithelial HeLa cells has revealed that in all cases the loss of virulence in the studied groups of mutants, resistant to antibiotics with different mechanisms of action (polymyxin M, mecillinam and neamin) was linked with the loss of the ability of bacteria to penetrate into epithelial cells. These changes are probably the result of disturbances in the structure of external membrane in polymyxin-resistant mutants, in the regulation of the penetration factor synthesis in mecillinam-resistant mutants, and in the translation process in neamin-resistant mutants.

[Multiplication dynamics in a pulmonary model of Sh. sonnei and Sh. flexneri differing in virulence].

The most essential differences in the time course proliferation of virulent and a virulent Sh. sonnei and Sh. flexneri strains in the pulmonary model were found to become, manifest 3--6--9 hours postinoculation.

[Differential characteristics of the I and II phases and R-form of Sh. sonnei].

Characteristics of various phases of Sh. sonnei were determined on the standard strains of Sh. sonnei of phases I and II and R-form used for the industrial production of agglutinating monoreceptor sera.