Restoration of virulence to rat of axenically grownEntamoeba histolyticaby cholesterol and hamster liver passage

Abstract

A virulent strain of E. histolytica (NIH-200) from a symptomatic human case, cultured in vitro for > 3 yr, was unable to infect rat cecum or hamster liver. When grown with a mixed bacterial flora, it infected rat cecum but did not produce ulceration. After passaging amoebae growing with bacteria in hamster liver, amoebic hepatic lesions were regularly produced. The amoebae from liver lesions produced ulceration in the ceca of rats. Exposure to cholesterol of amoebae growing with bacteria or feeding rats orally with cholesterol and injecting these amoebae along with bacteria also led to the production of ulcers in rats. Thus virulent amoebae which haye been cultured in vitro for a long time become attenuated, but their virulence can be revived.