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

Abstract

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) method because 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.