[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.

[Characteristics of the action of the biologically active factor from virulent Shigella flexneri strains in a study on mice and a cell culture].

The authors subjected to further study the biologically active factor revealed by them earlier in the virulent Sh. flexneri cultures by using the genetically bound triad of Sh. flexneri 5a-222 cultures and the corresponding couple of Sh.

[Comparative characteristics of cell-free filtrates of Shigella flexneri of different virulence].

It was shown for the first time that the virulent Sh. flexneri strain grown on Luria broth differed from the avirulent one by the yield of readily released surface-located complexes--lipopolysaccharide (determined by rhamnose) and protein into the filtrate. There was no distinct correlation between the strain virulence and the content of rhamnose-determined lipopolysaccharide in the filtrate; growing bacteria in the presence of Ca and Mg ions had no significant influence on the lipopolysaccharide release into the filtrate.

[Biological activity of extracts isolated from a virulent strain of Sh. flexneri grown in the presence of calcium ions].

The authors carried out a comparative study of the genetically connected Sh. flexneri cultures (3 virulent strains, 3 clones of an avirulent mutant selected in the flux of an oblique light from the virulent strain, and lac+ Kcp A-hybrids obtained by crossing the initial virulent cultures with the E. coli K12 Hfr strains).