Detection of ToxigenicCorynebacterium diphtheriaeandCorynebacterium ulceransStrains by a Novel Real-Time PCR

Detection of Toxigenic Corynebacterium diphtheriae and Corynebacterium ulceransStrains by a Novel Real-Time PCR ᰔ Diphtheria is caused by both toxigenic Corynebacterium diphtheriae and Corynebacterium ulcerans strains harboring lysogenic, tox-bearing beta-corynephages.While C. diphtheriae has caused most diphtheria cases for decades, the emerging pathogen C. ulcerans is becoming the major cause for diphtheria in many industrialized countries.Among the 25 Diphtheria Surveillance Network (DIPNET) members, Germany reported the most C. ulcerans-associated diphtheria patients after the United Kingdom and France (7).In C. diphtheriae, tox encodes diphtheria toxin (DT), causing the systemic diphtheria symptoms.Recently, we described nucleotide and amino acid sequence differences between the C. diphtheriae and C. ulcerans DTs (11).tox and DT in C. ulcerans are much more heterogenous than in C. diphtheriae (6), since the 11 published C. ulcerans tox and DT sequences fall into five different groups (4, 8, 9, 11).The differences between C. diphtheriae tox and C. ulcerans tox allow their differentiation by PCR (11), and a conventional C. diphtheriae tox PCR used by many laboratories worldwide for the identification of toxigenic corynebacteria amplifies both C. diphtheriae and C. ulcerans tox (2).Disturbingly, Tiwari et al. reported that a real-time C. diphtheriae tox PCR (5) used at the CDC caused atypical or false-negative results for two C. ulcerans diphtheria patients (12).Similarly, Cassiday et al. very recently published a study on the failure of their real-time PCR in detecting C. ulcerans tox (1).Since a reliable real-time PCR for detecting toxigenic corynebacteria is urgently needed, we developed and evaluated a novel 5Ј-nuclease real-time PCR detecting both C. diphtheriae and C. ulcerans tox.