Recent reports from several EU countries indicate circulation of toxigenic Corynebacterium diphtheriae among refugees from Asia and Africa as well as children's deaths among indigenous populations. Toxigenic C. diphtheriae carriers pose a serious risk for unvaccinated persons and ones with low level of immunological protection, the number of which in Europe has increased. The International system of quality control revealed the poor state of laboratory diagnosis of diphtheria in EU. This is mostly due to the absence of simple, standard and reliable method of the diphtheria toxin (DT) detection. The common method for detecting the production of DT by corynebacteria, gel immunoprecipitation or Elek test is vulnerable, time consuming and laborious. PCR for DT gene detection cannot be used instead of the Elek test, since non-toxigenic toxin gene-bearing (NTTB) C. diphtheriae and C. ulcerans circulate worldwide. The aim of this study was development and evaluation of rapid immunochemical test for the detection of DT.
Methods & Materials
Lateral Flow Immunoassay (LFIA) strips were designed using monoclonal antibodies against DT. Two hundred and fifty of toxigenic, non-toxigenic C. diphtheriae, C. ulcerans and other corynebacteria isolated in Germany in 2019-2021 were tested for DT after 6 hours of growth on the WHO-recommended liquid nutrient medium.
Results
A complete convergence of the conventional method of DT detection - Elek test and the LFIA for all 250 isolates of diphtheria and non-diphtheria corynebacteria was observed. The use of the LFIA makes it possible to significantly simplify DT detection and reduce the time of analysis from 24-48 to 4-6 hours. Thus, the possibility of replacing the Elek test with the LFIA appears real.
Conclusion
The availability of such a simple and reliable method for DT detection will speed up and increase the accuracy of diphtheria diagnosis globally. The efficient diphtheria laboratory diagnosis will enable timely initiation of anti-diphtheritic treatment that will save lives, prevent the development of complications, as well as stop the spread of the disease through early initiation of preventive measures.
