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Intestinal Lumen and Mucosal Microclimate H⁺ and NH₃ Concentrations as Factors in the Etiology of Experimental Amebiasis

Axenically cultivated Entamoeba histolytica, trophozoites, strains HM-1:IMSS and HM-38, were suspended in solutions of NaCl, 330 mOsm, of varying pH and ammonium concentrations. Short-term viability was inversely proportional to the ammonia concentration of the medium and was independent of the ammonium concentration and pH. The NH₃-induced ameba killing was associated with a cellular alkalosis and cell swelling. While short-term trophozoite viability was unaffected by changes in the medium pH over the range 5.5–8.0, long-term viability was reduced by high pH, and of three pH values tested (6.27, 7.27, and 8.27), trophozoite growth was greatest at the lower value. Chemotaxis was observed in media over the pH range 5.5–8.0, and attenuated chemotaxis was observed in trophozoites in media containing NH₃ (0.1 mM). The cecal content total ammonia concentration and pH and the in vivo mucosal microclimate pH were measured in young adult male rats, hamsters, and gerbils. Ceca of the three rodent species were also inoculated with HM-38 trophozoites and 7 days later the cecal contents were studied for signs of amebic infection. Infections were absent in the rat, the species with highest luminal total ammonia concentration and mucosal microclimate pH. All gerbils were infected. This species had the lowest mucosal microclimate pH. The hamster, with the intermediate microclimate pH, had a low infection rate (1 of 5). It is proposed that when ammonium diffuses from the large intestinal lumen into a more basic mucosal microclimate, it is converted to ammonia, and the combination of this ammonia and the high microclimate pH threatens Entamoeba trophozoite viability and reduces the probability of a given ameba penetrating the mucus blanket and invading the mucosal epithelium.

Accepted for publication October 5, 1987.