Detection of diphtheria toxin production by toxigenic corynebacteria using an optimized Elek test,Infection

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Detection of diphtheria toxin production by toxigenic corynebacteria using an optimized Elek test
Infection ( IF 5.4 ) Pub Date : 2022-09-02 , DOI: 10.1007/s15010-022-01903-x
Vyacheslav G Melnikov ₁ , Anja Berger _{1,

2} , Andreas Sing _{1,

2}

Affiliation

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.

中文翻译：

使用优化的 Elek 测试检测产毒棒状杆菌产生的白喉毒素

目的

白喉在世界许多国家仍然存在，是由白喉棒状杆菌复合体的产毒菌株引起的，主要是白喉棒状杆菌和新出现的人畜共患病原体溃疡梭菌。根据 Elek 的免疫沉淀试验是检测产毒棒状杆菌中主要毒力因子白喉毒素 (DT) 的金标准。由于其复杂的方法要求，经典的 Elek 测试主要由专门的参考实验室执行。据透露，目前对 Elek 测试的修改无法检测到弱产毒分离株中的毒素。因此，迫切需要一种更稳健的检测游离 DT 的方法，尤其是对于产毒的溃疡念珠菌已知产生的 DT 量通常比白喉杆菌低得多的菌株。