Mechanism of antigenic variation in Shigella flexneri bacilli. III. Complement sensitivity of S. flexneri 1b strains and their 3b variants selected either as Lac+ recombinants or phage F2 resistant mutants.

Several S. flexneri 1b serotype strains of clinical isolation were compared with their 3b serotype variants isolated either as Lac+ recombinants from crosses of S. flexneri x E. coli Hfr C, or F2-resistant mutants. The studied variants 3b were deprived of type I antigen but acquired type III antigen. They appeared to be less sensitive to killing action of complement present in normal bovine serum although kinetics of killing and its effectiveness differed between the strains.