Virulence and toxicity of axenic Entamoeba histolytica

Abstract

THE ability of cultured Entamoeba histolytica to cause ulcers in the caecum of guinea pigs and rats or abscesses in the liver of the Syrian hamster decreases rapidly on elimination of the accompanying bacterial flora^1–4. It seemed that some strains grown axenicailly on TP-S-1 medium⁵ for many years had lost their pathogenicity entirely. When very large inocula were used, however, (10⁷ amoebae), a granulomatous lesion was evoked in the hamster liver^6,7. Our experiments with strains made freshly axenic, isolated from patients with amoebic dysentery, suggested that the number of amoebae required to induce a certain extent of pathology in the hamster liver increased with the number of transfers in axenic culture⁸. After a long period of axenic growth, strains probably maintain a very low degree of pathogenicity. Using two such strains, HK-9 and HB-301, we obtained results which may contribute to the understanding of the pathogenicity of E. histolytica. We were aible to restore the virulence of the HK-9 strain with cholesterol and establish a higher degree of virulence by two successive passages through hamster liver (HK-9H>₂). In vitro toxicity towards guinea pig leukocytes, and agglutinability induced by concanavalin A (con A) were markedly greater in strain HK-9H₂ than in HK-9. Antigenic analysis revealed a pattern for HK-9H₂, different from that of the HK-9 strain.