Cell Biological, Epidemiological and Clinical Studies on Entamoeba dispar infection

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As Entamoeba histolytica was reclassified into pathogenic ameba, Entamoeba histolytica, and nonpathogenic one, Entamoeba dispar in 1997, a variety of aspects of these amebae and their infection needed to be reassessed. Accordingly studies on E. dispar infection was attempted. ? Axenic cultivation of E. dispar could be produced with C. fasciculata treated at high temperature and subsequently with hydrogen peroxide, as a culture associate. ? Monoclonal antobodies and their Fab fragments useful for identification of both amebae were produced. ? To clarify the biological properties, metabolism of sulfur-containing aminoacids was investigated. The gene encoding ATP sulfurylase was cloned from E. histolytica and its recombinant protein was characterized. Moreover, the gene encoding cysteine synthase was closed from E. dispar, which demonstrated the presence of two isoforms. Serine acetyltransferase, a regulatory enzyme of cysteine biosynthesis, was also studies by similar approach for both species of amebae, and the properties investigated. These studies clearly demonstrate amebae were the first eukaryote which has a functional cysteine biosynthetic pathway. ? With E. histolytica and E. invadens as a model, a variety of inhibitors were examined for the potential to suppress the growth. Consequently, dinitroaniline herbicides and cytochlasin D were found to inhibit in vitro growth and encystation of the model. ? By epidemiological analysis, only E. histolytica was detected from institutionalized population though all of them were asymptomatic.