The toxigenic strains of organisms in the Corynebacterium diphtheriae complex, primarily Corynebacterium diphtheriae and the newly developing zoonotic pathogen C. ulcerans, are what cause diphtheria, which is still widespread around the world. According to Elek, the immunoprecipitation test is the industry standard for identifying toxicogenic corynebacteria's main virulence factor, diphtheria toxin (DT). The traditional Elek test is mostly carried out by professional reference laboratories due to its complex methodological requirements. It was discovered that mildly toxigenic isolates cannot be detected by the Elek test with its current configuration. Therefore, it is urgently necessary to develop a more reliable method for detecting free DT, particularly for toxicogenic C. ulcerans strains, which are known to frequently produce DT in considerably lower concentrations than C. diphtheriae.

In this study, 31 C. ulcerans isolates previously identified as NTTB (non-toxigenic tox bearing) with a positive standard Elek test result were re-analyzed using a modified immunoprecipitation method that was optimised for a variety of factors, including the type and concentration of antitoxin, medium volume, inoculum distance from the antitoxin disc, and position of controls.

The most significant pathogens of the Corynebacterium diphtheriae complex that cause diphtheria and diphtheria-like illness in humans are strains of the classical diphtheria agent Corynebacterium diphtheriae that produce the diphtheria toxin (DT), as well as the emerging zoonotic species Corynebacterium ulcerans. Only toxigenic strains can produce classical respiratory or cutaneous diphtheria; non-toxigenic strains cannot, as the phage-encoded DT is the virulence factor responsible for generating diphtheria symptoms, such as pseudomembrane development or cardiac and neurological sequelae. Therefore, it is crucial to identify toxic Corynebacterium strains in diphtheria laboratory-based diagnosis, both for patient management and for public health actions. Today, PCR makes it simple to find the tox gene that codes for DT.