Increase of DNA content in tissue stages ofEntamoeba histolytica strain SFL 3

The DNA content of culture forms and tissue stages of pathogenicE. histolytica strain SFL 3 were measured photometrically after the nuclei had been stained with the fluorochrome BAO. As a control, the DNA guartity ofE. histolytica strain HK 9 andE. invadens were determined by the same method and compared with reference values. Tissue stages were obtained from hamsters experimentally infected by intrahepatic injection of SFL 3 amoebae. Further studies concerning possible changes in the DNA content of tissue stages involved the following methods: (a) isolation of tissue stages from the liver, followed by distinct suspension periods. (b) Infected liver pieces were directly transferred into culture medium; amoebae emigrating therefrom were cultivated. The study demonstrated that tissue stages contained up to 4 times more DNA than did culture forms. After 3 h cultivation, the DNA content of tissue stages decreased to the level of culture forms. Possible reasons for this change are discussed.