Immunologic methods for the detection of diphtheria toxin (passive hemagglutination and ELISA for toxin detection in cultures and serum)

A competitive passive hemagglutination assay (cPHA) easy to perform and a highly sensitive ELISA have been investigated for detection of diphtheria toxin from cultures and from human serum. The sensitivity of the cPHA (8 ng toxin/ml) was high enough to detect toxin in pure cultures containing C. diphtheriae. For this application the cPHA proved to be a simple and reproducible alternative to the Elek-Ouchterlony test. Toxin in culture filtrates of nasal and tonsillar swabs containing toxinogenic strains of C. diphtheriae together with germs of the physiological flora and toxin in serum can be detected with the more sensitive Biotin/Streptavidin ELISA (0.6 ng toxin/ml). This allows the confirmation of the clinical diagnosis "diphtheria" within 24-48 h.