The effect of axenic versus xenic culture conditions on the total and secreted proteolytic activity of Entamoeba histolytica strains.

Proteolytic activity was measured in lysates of four axenic and five xenic cultures of different strains of pathogenic E. histolytica, and in five non-pathogenic strains ("E. dispar") growing in xenic culture. There was no significant difference in total proteolytic activity, using either gelatin or albumin as substrate, between the two sets of xenic cultures; the axenic pathogens however had significantly higher levels of activity than the xenic pathogens, the levels appearing to correlate with virulence. An axenic strain (NIH 200) reassociated with mixed bacterial flora reverted to close to xenic levels of activity. There was no evidence of secretion of an elevated proportion of the total enzymic activity by pathogenic strains, and expression levels may owe more to culture conditions than to genotype.