Automatic and manual latex agglutination tests for measurement of cholera toxin and heat-labile enterotoxin of Escherichia coli

Abstract

Automated and manual latex agglutination methods were employed to measure cholera toxin (CT), heat-labile enterotoxin (LT) of Escherichia coli, and their subunits A and B. Dow polystyrene latex particles (diameter, 0.22 μm) and polystyrene-chlorostyrene latex particles (diameter, 1 μm) were sensitized by rabbit-specific immunoglobulin for each antigen and used as the reagents of the automated and manual agglutination tests, respectively. Automated agglutination was performed by a nephelometric assay system measuring time-dependent differences of light scattering due to agglutination, and manual latex agglutination was carried out in microtiter plates. As low as 1,000 and 31 pg of CT per ml were estimated by the automated and manual agglutination tests, respectively. Using these methods, the amount of CT and LT was measured in several clinical isolates of Vibrio cholerae and E. coli. Furthermore, it was discovered that cyclic AMP is not essential for the production of CT by measuring the amount of the toxin in numbers of cyclic AMP-dependent mutants of V. cholerae (with the agglutination tests).