Heat-labile enterotoxin can be released from Escherichia coli cells by host intestinal factors.

The heat-labile enterotoxin (LT) of Escherichia coli is localized in the periplasm of the bacterial cell. Growth of an LT-producing strain of E. coli in the presence of bile salts, in concentrations within the range found in the human small intestine, caused leakage of LT into the culture medium. This leakage could be augmented by the presence in the medium of trypsin and by minimizing the concentration of free iron.