Related Experiment Video
Updated: Aug 30, 2025
Enrichment and Detection of Clostridium perfringens Toxinotypes in Retail Food Samples
Published on: October 18, 2019
Detection of diphtheria toxin production by toxigenic corynebacteria using an optimized Elek test
Vyacheslav G Melnikov1, Anja Berger1,2, Andreas Sing3,4
1National Conciliary Laboratory on Diphtheria, Veterinärstraße 2, 85764, Oberschleißheim, Germany.
Purpose:
Diphtheria, still present in many countries of the world, is caused by toxigenic strains of species of the Corynebacterium diphtheriae complex, mainly Corynebacterium diphtheriae and the emerging zoonotic pathogen C. ulcerans. The immunoprecipitation test according to Elek is the gold standard for detection of the major virulence factor diphtheria toxin (DT) in toxigenic corynebacteria. Due to its sophisticated methodological requirements, the classical Elek test is performed mainly by specialized reference laboratories. It was revealed that the current modification of the Elek test does not detect the toxin in weakly toxigenic isolates. Therefore, a more robust method for detecting free DT is urgently needed, especially for toxigenic C. ulcerans strains which are known to produce often much lower amounts of DT than C. diphtheriae.
Methods:
Thirty-one tox-positive C. ulcerans isolates with a negative standard Elek test result previously determined as NTTB (non-toxigenic tox bearing) were re-analyzed in this study using a modified immunoprecipitation method optimized regarding different parameters including type and concentration of antitoxin, medium volume, inoculum distance from the antitoxin disk and position of controls.
Results:
All 31 C. ulcerans strains tested positive in the optimized Elek test.
Conclusion:
Only with a reliable and easy-to-handle method for detecting the toxigenicity of C. ulcerans, it is possible to assess the etiological role of this emerging zoonotic bacterium in human pathology.
