Polymorphisms of dtxR Gene of Corynebacterium diphtheriae Isolated from Diphtheria Outbreak in Indonesia

Background: In Corynebacterium diphtheriae, the dtxR gene plays a role in regulating diphtheria toxin synthesis. The dtxR gene is often used as a marker for identifying C. diphtheriae by the polymerase chain reaction (PCR)methodbecause it is present in all strains of this bacterium. Mutations in the dtxR gene can cause the over-synthesis of diphtheria toxin and reduce PCR assays’ sensitivity. Objectives: This study aimed to describe the polymorphisms in the dtxR gene of C. diphtheriae isolated from a diphtheria outbreak in Indonesia. Methods: Forty-eight isolates of C. diphtheriae were obtained from clinical samples (throat/nasopharyngeal swabs) of diphtheria cases and close contacts. The isolates were revived on a blood agar plate (BAP), bacterial colonies were harvested, and deoxyribonucleic acid (DNA) was extracted. The DNA sequencing was carried out using a Whole-genome Sequencing (WGS) approach. The data were converted and analyzed with U-gene software. The dtxR gene analysis was performed with C. diphtheriae PW8 as references. Results: There were 59-point mutation locations in 48 isolates examined. None of these single nucleotide polymorphisms (SNPs) coded for amino acid changes. Based on the mutation pattern, seven clades/groups of the dtxR gene of 48 C. diphtheriae isolates were examined. Conclusions: At least seven types of DNA sequences and more than 50 SNPs of the dtxR gene were identified in 48 C. diphtheriae isolates from a diphtheria outbreak in Indonesia. Although all of them are silent mutations, they must be considered in the design of PCR examination in diphtheria laboratories.