Effect of phosphatidylcholine–cholesterol liposomes on Entamoeba histolytica virulence

Trophozoites of Entamoeba histolytica HM-1:IMSS become less virulent after long-term maintenance in axenic cultures. The factors responsible for the loss of virulence during in vitro cultivation remain unclear. However, it is known that in vitro cultivation of amoeba in culture medium supplemented with cholesterol restores their virulence. In this study, we analyzed the effect of adding phosphatidylcholine–cholesterol (PC–Chol) liposomes to the culture medium and evaluated the effect of this lipid on various biochemical and biological functions of E. histolytica HM-1:IMSS in terms of its virulence. The addition of PC–Chol liposomes to the culture medium maintained the virulence of these parasites against hamster liver at the same level as the original virulent E. histolytica strain, even though these amoebae were maintained without passage through hamster liver for 18 months. The trophozoites also showed increased endocytosis, erythrophagocytosis, and carbohydrate residue expression on the amoebic surface. Protease activities were also modified by the presence of cholesterol in the culture medium. These findings indicate the capacity of cholesterol to preserve amoeba virulence and provide an alternative method for the maintenance of virulent E. histolytica trophozoites without the need for in vivo procedures.

Parasitological and serological studies on Amoebiasis and other intestinal parasitic infections in Recife and its suburban area, northeast Brazil

Parasitological examinations were carried out during April to August, 1987, with 187 out-patients of the IMIP hospital, located in the center of Recife City, and 464 inhabitants of several villages around Cabo City, 50 Km southeast of Recife, Pernambuco, Brazil. Approximately 71% of the IMIP patients and 92% of the Cabo inhabitants were infected with at least one species of intestinal parasite. There was minimum difference in the prevalence rate of Trichuris trichiura between two areas, whereas the prevalence rates of Ascaris lumbricoides, hookworms, Strongyloides stercoralis, Schistosoma mansoni and Entamoeba histolytica were higher in the inhabitants of the Cabo City area. Only Giardia lamblia was more prevalent in the out-patients of IMIP hospital. Test tube cultivation revealed that the prevalence rate of Necator americanus in both areas was much higher than that of Ancylostoma duodenale , and also that the prevalence rate of S. stercoralis of the IMIP patients and Cabo inhabitants were 4.5% and 9.6%, respectively. Six hundred and fifteen sera were serologically examined for amoebiasis by the gel diffusion precipitation test (GDP) and enzyme linked immunosorbent assay (ELISA) using the antigen prepared from axenically cultured trophozoite of E. histolytica (strain HM-ITMSS). No positive reaction was observed in all of the sera as examined by GDP, while 32 out of 615 sera were positive on ELISA.

Entamoeba histolytica: the effect of different culture conditions on the components of amoebic movement

The behaviour of trophozoites of Entamoeba histolytica, strain IP-106, were examined under three sets of culture conditions: various acid pH values, cysteine concentrations, and dilutions of bile. Changes in amoebic behaviour, as compared with controls, were evident under conditions of the lowest pH value tested (pH 5.1), at the highest cysteine concentration tested (17 mM), and at both dilutions of bile assayed. These changes in behaviour were due to a modulation of two components of amoebic movement, the rate of activity and (or) the rate of change of direction. These changes are thought to be the results of "metabolic" and "kinetic" effects, respectively, on these two parameters.

Entamoeba histolytica: the dynamics of penetrating a meniscus

Using a closed-circuit television system, Entamoeba histolytica strain IP-106 was observed to penetrate through a meniscus separating a medium–nitrogen gas interface. Both the forces exerted on the amoeba by the surface tension of the liquid medium and the resultant forces applied by the amoeba, at various stages during penetration, were calculated. During penetration the force applied increased to a maximum of 3.3 × 10−6 N. However it was found that the shape of the amoeba allowed it to penetrate with a constant pressure. Intercellular movement due to active pseudopodial motion may play an important role in the process of penetration.