Intestinal lumen and mucosal microclimate H+ and NH3 concentrations as factors in the etiology of experimental amebiasis
Leitch, G.J.
American Journal of Tropical Medicine and Hygiene 38(3): 480-486
1988
ISSN/ISBN: 0002-9637 PMID: 2908580 Document Number: 315832
Axenically cultivated Entamoeba histolytica trophozoites (strains HM-1:IMSS and HM-38) were suspended in solutions of NaCl, 330 mOsm, of different pH and ammonium concentrations. Short-term viability was inversely proportional to [NH3] of the medium and was independent of [NH4+] and pH. The NH3-induced amoeba killing was associated with a cellular alkalosis and cell swelling. Short-term trophozoite viability was unaffected by changes in the medium pH over the range 5.5-8.0, but long-term viability was reduced by high pH, and of 3 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 nM). The caecal content total ammonia concentration and pH and the in vivo mucosal microclimate pH were measured in young adult male rats, hamsters and gerbils. Caeca of the 3 rodent species were also inoculated with HM-38 trophozoites and 7 days later the caecal contents were studied for signs of amoebic 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 reduces Entamoeba trophozoite viability and reduces the probability of a given amoeba penetrating the mucus blanket and invading the mucosal epithelium.