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Biological Studies on Endamoeba Histolytica

I. The Growth Cycle of Populations in a Mixed Bacterial Flora¹

Growth of E. histolytica was traced in the culture media of Cleveland and Collier, Dobell and Laidlaw, and Balamuth and Sandza. The growth curves of amoebae and bacteria followed the classical bacterial pattern, although higher yields and greater change in pH occurred in the richer media. The lag phase of amoebic growth was relatively prolonged in comparison to bacterial growth. The data suggest a conditioning effect of the bacterial flora on the medium rendering it more suitable for amoebic growth.

Analysis by means of growth curves permitted the demonstration that rice starch had a specific growth-promoting influence on amoebae in late stages of cultivation, even though bacterial growth continued to decline.

Experiments showed that the lag phase of amoebic growth was shortened in media preconditioned by growth of bacteria alone. The data in general suggest the stimulation of amoebic growth by a heat-stable factor (or factors) produced by bacterial metabolism.

¹ This investigation was supported by a grant from the Abbott Fund of Northwestern University.