Immunological Differentiation of Shigella Alkalescens from Shigella paradysenteriae Flexner, V, W, X, Y, and Z

When Andrewes described for the first time a new member of the Shigella group that is referred to today as Shigella alkalescens, his main purpose was to differentiate this microörganism from true dysentery bacilli. The purpose of this differentiation still holds true, since Shigella alkalescens does not cause epidemic or endemic forms of bacillary dysentery in man as does the closely related Shigella paradysenteriæ Flexner. Both microörganisms show similarities, not only in cultural characters but also in antigenic structure: Shigella alkalescens may be agglutinated by anti-Flexner sera and anti-Shigella alkalescens sera may agglutinate certain strains of Shigella paradysenteriæ Flexner as demonstrated by Andrewes, Smith and Fraser, Popoff and Spanswick, Welch and Mickle, Gilbert and Coleman, Neter and Rappole, and Neter., Recently, it was found that type-specific anti-Shigella paradysenteriæ Flexner sera differ markedly in their content of cross-agglutinins for Shigella alkalescens. While anti-Shigella paradysenteriæ Y sera strongly agglutinated Shigella alkalescens, and anti-Shigella Paradysenteriæ V and X sera contained a moderate titer of agglutinins for this microörganism, anti-Shigella paradysenteriæ W and Z sera may lack agglutinins for Shigella alkalescens in spite of a high titer of agglutinins for the respective, homologous types of Shigella paradysenteriæ Flexner. It could be shown that certain strains of Shigella paradysenteriæ Flexner absorbed their cross-agglutinins from anti-Shigella alkalescens sera, and that such absorbed sera still agglutinated Shigella alkalescens. It is well known that it is not possible to absorb completely anti-Shigella paradysenteriæ Flexner sera with heterologous types of the Flexner group. The possibility has to be considered, that Shigella alkalescens may contain several antigenic components in common with certain types of the Flexner group and that the absorption of anti-Shigella alkalescens serum with only one type of the Flexner group may not remove all anti-Flexner agglutinins.