ENTAMOEBA-HISTOLYTICA CYSTS WITH A DEFECTIVE WALL FORMED UNDER AXENICCONDITIONS

Axenic HK9 Entamoeba histolytica strain amoebae, maintained in PEHS me dium, displayed several cystic characteristics that involve an active process of cystic wall formation, cellular volume and density diminuti on, and one or two nuclear divisions. The differentiation process was asynchronic, beginning after the logarithmic growth phase. The axenic cysts, which were maintained in a 50 mOsm/kg medium at 4-degrees-C for 72 h, produced growing trophozoites within 1 7 days of incubation at 36-degrees-C in fresh medium. Negative results were obtained with trop hozoites submitted to the above treatment, and with axenic cysts maint ained in double-distilled water at 4-degrees-C for 24 h, or in 0.1 % s arkosyl, for 10 min at room temperature instead of 55 mosmol/kg medium . Thus, the HK9 E. histolytica strain, cultured in PEHPS, produced und er axenic conditions a small proportion of mature, metabolically activ e cysts, but with an immature or abnormal wall.