To explore the mechanism of development of healthy carrier state of dysentery bacilli, the virulence has been compared among Shigella strains freshly isolated from dysentery patients and healthy carriers and the old laboratory strains. The virulence was principally determined using infection models for shigellosis, that is, the abilities to produce keratoconjunctivitis in guinea pigs (KC-reaction) and to multiply intracellularly in HeLa-S3 cell cultures, along with the tests for cytopathic effect on cultured cells, for mouse virulence as determined by intraperitoneal injection with mucin and for acid agglutinability.
Freshly isolated strains of Shigella both from dysentery patients and from carriers were equally capable to produce KC-reaction and to multiply intracellularly, whereas these capacities were found to be lost in the majority of the laboratory strains. Cytopathic effect on HeLa cells, mouse virulence and acid agglutinability of the strains presently examined proved not to show any significant parallelism with the capacities to produce KC-reaction or to multiply intracellularly. On the basis of our present findings, it seems very likely that the Shigella strains isolated from healthy carriers are as pathogenic as those from dysentery patients.
The usefulness of various tests for the study on the pathogenesis of dysentery has also been discussed.