Evaluation of Conventional PCR for Detection of Toxigenic Corynebacterium diphtheriae Strains in Malaysia

Diphtheria is an infectious but vaccine preventable disease caused by Corynebacterium diphtheriae and humans are the only reservoir. While toxigenic strains most frequently cause pharyngeal diphtheria, non-toxigenic strains commonly cause cutaneous infections. In 2016, there was a sudden increase in cases of C. diphtheriae reported in Malaysia. The toxigenic strains are currently determined using Elek's test and are carried out only in the reference laboratory. With the sudden increase in diphtheria cases in Malaysia, it is important for local laboratories in state hospitals to be able to perform a rapid, reliable diagnostic test for the detection of the exotoxin. In this study, we aimed to evaluate the application of conventional PCR method to detect toxigenic strains of C. diphtheriae compared to the Elek's test. Forty-eight C. diphtheriae strains were subjected to PCR detection of toxin gene A and B subunits, and also Elek's test. The A and B subunits of the toxin gene were detected in all C. diphtheriae strains except for one strain which was isolated from a foot ulcer. Elek's test was also positive for all the PCR positive strains. This study showed 100% corelation between the results of PCR and Elek's test assay. The conventional PCR can be used at the state laboratories for rapid detection of toxin genes in toxigenic C. diphtheriae cultures, thus early treatment can be given to the patients while waiting for Elek's test results.