Date of Award


Degree Type


University or Center

Atlanta University (AU)

Degree Name




First Advisor

Dr. Gordon J. Leitch


Entamoeba histoiytica trophozoites must enzymatically degrade or physically penetrate the intestinal mucus blanket when this parasite changes from a commensal to an invasive enteropathogen. When axenically cultivated E. histolytica trophozoites, strain HM-1:IMSS, were inoculat ed into rat colon, the motility of amebae attached to mucus fragments was decreased and those free in luminal fluid increased. In the mucus glycoprotein, mucin, ameba motility was increased at low concentrations and decreased at high concentrations. Of the three mucin end group carbo hydrates, N-acetylneuraminic acid stimulated motility, L-fucose was inhibitory and N-acetylgalactosamine was slightly inhibitory, but only at high concentrations. N-acetylneuramin-lactose and mucin, which are N-acetylneuraminic acid containing compounds, stimulated ameba motility.

E. histolytica was found to possess a membrane associated neuraminidase, with a pH optimum of 6.7. More than 50% of the enzyme was localized on the plasma membrane. Both ameba neuraminidase activity and motility required Ca++ and were inhibited by cytochalasin D. This microfilament disruptor caused redistribution of neuraminidase and two other membrane associated enzymes, Ca++-ATPase and p-nitrophenyl phosphatase from the plasma membrane to intracellular membranes. The ameba was also found to possess a soluble type 1 N-acetylneuraminic acid aldolase with pH optimum of 7.4. When the force required for ameba to physically penetrate rat mucus was measured, results suggested that the trophozoites could penetrate rat cecal mucus but not colonic mucus. Due to differences in the physical properties of mucus in different parts of the intestine and the role of N-acetylneuraminic acid in determining the rate of mucin degradation by bacteria, it is postulated that E^ histolytica trophozoites may either enzymatically degrade or physically penetrate the mucus blanket when invading the large intestine.

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