Maintenance of integrity, viability, and adhesion of Entamoeba histolytica trophozoites in different incubation media.

We have determined the integrity, viability and adhesion of Entamoeba histolytica HK9 and HM1 trophozoites during their incubation in two basal culture media (TP and TYI) and three saline media ("maintenance medium" MM-1 and two others buffered with HEPES). In basal culture media, more than 70% of the trophozoites maintained their integrity and adhesion to human red blood cells (RBC) for up to 4 h, and the proportion of those excluding Trypan blue decreased slowly after 2 h. In saline media, the number of ameba-RBC complexes reached a maximum after 20-30 min and then decreased rapidly (and fastest in MM-1), less than 10% of the amebae were intact after 3-4 h, and dye exclusion fell abruptly from the start of incubation. The number of ameba-RBC complexes formed and the rate of adhesion were highest in basal TP medium. Normal nonvacuolated refringent (NVR) trophozoites deteriorated progressively in all media--although much faster in the saline ones--to vacuolated refringent (VR), nonrefringent, and disrupted. Trypan blue was excluded by all NVR and a fraction of the VR trophozoites. Horse serum helped to maintain ameba integrity and viability, but inhibited adhesion in a concentration-dependent manner. We conclude that E. histolytica trophozoite integrity and adhesion are adequately preserved and should be characterized only in basal culture media, that refringence without vacuolization is a more stringent characteristic of ameba quality than Trypan blue exclusion, and that some serum component inhibits ameba adhesion.