IN-VITRO ASSAYS FOR DETECTION OF DIPHTHERIA-TOXIN

Subunit-specific antipeptide antibodies have been used to develop a do t blot immunoassay for detection of diphtheria toxin (DT) produced by toxigenic strains of Corynebacterium diphtheriae. A detection limit of 0.1-1.0 ng DT/ml was obtained. DT is cytotoxic to cultured vero cells and cell viability if conveniently assessed using a tetrazolium dye, MTT. This has been used as the basis of a cytotoxicity assay for DT, w hich has a detection limit of 20 pg/ml of biologically active toxin. S ixty isolates of C. diphtheriae were assayed for toxigenicity. There w as complete concordance between the Vero cell cytotoxicity assay and g uinea pig intradermal assay in vivo, demonstrating the utility of the cytotoxicity assay.