Isolation and characteristics of Shigella sonnei donor strains

: The possibility of obtaining Sh. sonnei donor strains in phases I and II by two methods is shown: by the transfer of the distal market lac+ from E. coli K12, Hfr-strain P4X, or by using F'ts lac+ episome. Of 5 Sh. sonnei donor strains in phase I, obtained by hybridization with E. coli K12, Hfr-strain P4X, 3 strains retained their virulence, in contrast to Sh. flexneri donor strains in the S-form, previously obtained by similar hybrizations. Of 8 Sh. sonnei donor strains in phase I, obtained by hybrididization with E. coli K12 KS 881, 6 strains were virulent. Sh. sonnei donor strains in phases I and II obtained in these experiments lost their fertility after being kept on the Dorset egg medium at 4 degrees C for 1.5--2 months.