Quantitative analysis of the production of heat-labile enterotoxin by enterotoxigenic Escherichia coli.

A modified method of passive immune hemolysis (PIH) was applied to the quantitative assay of heat-labile enterotoxin (LT) produced by enterotoxigenic Escherichia coli. The method enabled the measurement of 0.2 to 1.2 ng LT. The production of LT by enterotoxigenic E. coli under various conditions was analyzed using the modified method. LT production was intense during the logarithmic growth phase and decreased during the stationary growth phase. Lincomycin (50 to 100 micrograms/ml) affected cell growth slightly, but enhanced production of LT until the late-stationary growth phase. About 90% of the LT produced was retained in the cell, and the rest was excreted into the culture medium. The initial pH of the culture medium affected LT production. Alkaline pH enhanced LT production, though growth was depressed. Aeration enhanced both growth and LT production.