The association of axenically grown trophozoites of Entamoeba histolytica strains HK-9 or HM-1:IMSS with various types of gram-negative bacteria for relatively short periods markedly increased their virulence, as evidenced by their ability to destroy monolayers of tissue-cultured cells. Interaction of trophozoites with bacteria that were heat inactivated, glutaraldehyde fixed, or disrupted by sonication, or bacteria treated with inhibitors of protein synthesis, did not augment amebic virulence. Lethally irradiated bacteria, however, retained their stimulative properties and trophozoites that ingested bacteria were protected from the toxic effects of added hydrogen peroxide. An increase in virulent properties of amebae was also found in experiments carried out under microaerobic conditions (5% O2, 10% CO2). The augmentation of amebic virulence due to association with bacteria was specifically blocked by metronidazole, but not by tetracycline or aminoglycosides, and the rate of metronidazole uptake in stimulated trophozoites was two to three times higher. The results obtained suggest that virulence of axenically grown E. histolytica trophozoites may depend to a considerable extent on the cell's reducing power. Both microaerobic conditions and the association with bacteria apparently stimulate the electron transport system of the ameba. Bacteria may function as broad range scavengers for oxidized molecules and metabolites through the contribution of enzymatic systems, components, or products.

https://rupress.org/jem/article-pdf/160/2/353/1393805/353.pdf

Virulence of Entamoeba histolytica trophozoites. Effects of bacteria, microaerobic conditions, and metronidazole.

Acanthamoeba interactions with human brain microvascular endothelial cells.

Entamoeba histolytica virulence is related to a number of amebic components (lectins, cysteine proteinases, and amebapore) and host factors, such as intestinal bacterial flora. Trophozoites are selective in their interactions with bacteria, and the parasite recognition of glycoconjugates plays an important role in amebic virulence. Long-term monoxenic cultivation of pathogenic E. histolytica trophozoites, strains HK-9 or HM-1:IMSS, with Escherichia coli serotype O55, which binds strongly to the Gal/GalNAc amebic lectin, markedly reduced the trophozoites' adherence and cytopathic activity on cell monolayers of baby hamster kidney (BHK) cells. Specific probes prepared from E. histolytica lectin genes as well as antibodies directed against the light (35-kDa) and heavy (170-kDa) subunits of the Gal/GalNAc lectin revealed a decrease in the transcription and expression of the light subunit in trophozoites grown monoxenically with E. coli O55. This effect was not observed when E. histolytica was grown with E. coli 346, a mannose-binding type I pilated bacteria. Our results suggest that the light subunit of the amebic lectin is involved in the modulation of parasite adherence and cytopathic activity.

Down regulation of Entamoeba histolytica virulence by monoxenic cultivation with Escherichia coli O55 is related to a decrease in expression of the light (35-kilodalton) subunit of the Gal/GalNAc lectin.

The antiamoebic effect of a crude drug formulation of herbal extracts against Entamoeba histolytica in vitro and in vivo.

Amebiasis, a significant cause of morbidity and mortality on a global scale, is caused by invasion of the colonic mucosa by the cytolytic protozoan parasite Entamoeba histolytica. A review of the investigations into the mechanisms by which the parasite causes invasive disease is presented, including the relevant history, epidemiology, and pathology of amebiasis, the biology of the parasite, in vivo and in vitro studies of the pathogenesis of disease, the host immune responses, and possibilities for prevention and biologic control. New insights into the cell biology of E. histolytica, especially its adherence and cytolytic properties, offer several new approaches to biologic control of this invasive, destructive parasitic infection.

A Review of the Parasite Cellular Mechanisms Involved in the Pathogenesis of Amebiasis

A virulent strain of Entamoeba histolytica (NIH-200) from a symptomatic human case, cultured in vitro for more than three years, was unable to infect rat caecum or hamster liver. When grown with a mixed bacterial flora, it infected rat caecum but did not produce ulceration. After passaging amoebae growing with bacteria in hamster liver, amoebic hepatic lesions were regularly produced. The amoebae from liver lesions produced ulceration in the caeca of rats. Expoxure to cholesterol of amoebae growing with bacteria or feeding rats orally with cholesterol and injecting these amoebae along with bacteria also led to the production of ulcers in rats. Thus virulent amoebae which have been cultured in vitro for a long time become attenuated but their virulence can be revived.

Restoration of virulence to rat of axenically grown Entamoeba histolytica by cholesterol and hamster liver passage.

Repeated passage of the 200-NIH strain of Entamoeba histolytica through cholesterol-enriched axenic growth medium induced marked increases in cholesterol, phosphoglucomutase and hexokinase levels and a less prominent rise in the protein content of amoebic cells. There was also pronounced enhancement of haemolytic activity and Concanavalin A (Con A) agglutinability of the culture, but no significant change was observed in glucose phosphate isomerase. These cholesterol-induced effects persisted to a large extent when amoebae were subsequently repassaged through normal axenic medium lacking exogenous cholesterol, but changes in cellular cholesterol and protein levels did not persist. Qualitatively similar results were obtained whether the sterol was layered as a film on the glass walls of the culture tubes or supplied as sonicated micells, but the latter was in general more effective.

Cholesterol induced changes in glucose-6-phosphate generating enzymes, concanavalin A agglutinability and haemolytic activity of axenic Entamoeba histolytica.

Quantitatively much higher Concanavalin A (Con. A) agglutinability, haemolytic potency, and activities of acid hydrolases, namely phosphatase (EC 3.1.3.2), ribonuclease (EC 2. 7. 7.16), deoxyribonu...

Evidence for selection of virulent sub-populations of Entamorba histolytica by cholesterol

Les activites hydrolase a pH alcalin (9) sont plus faibles comparees aux valeurs observees a pH acide (5) et ne sont pas alterees par le cholesterol

S. R. Das

Papers

Restoration of virulence to rat of axenically grown Entamoeba histolytica by cholesterol and hamster liver passage.

Cholesterol induced changes in glucose-6-phosphate generating enzymes, concanavalin A agglutinability and haemolytic activity of axenic Entamoeba histolytica.

Evidence for selection of virulent sub-populations of Entamorba histolytica by cholesterol

Action of cholesterol on virulence related biochemical functions of Entamoeba histolytica.