Molecular characterization of Corynebacterium diphtheriae isolates in Malaysia between 1981 and 2016

Genomic characterization of cocirculating Corynebacterium diphtheriae and non-diphtheritic Corynebacterium species among forcibly displaced Myanmar nationals, 2017-2019

Respiratory diphtheria is a serious infection caused by toxigenic Corynebacterium diphtheriae, and disease transmission mainly occurs through respiratory droplets. Between 2017 and 2019, a large diphtheria outbreak among forcibly displaced Myanmar nationals densely settled in Bangladesh was investigated. Here we utilized whole-genome sequencing (WGS) to characterize recovered isolates of C. diphtheriae and two co-circulating non-diphtheritic Corynebacterium (NDC) species - C. pseudodiphtheriticum and C. propinquum. C. diphtheriae isolates recovered from all 53 positive cases in this study were identified as toxigenic biovar mitis, exhibiting intermediate resistance to penicillin, and formed four phylogenetic clusters circulating among multiple refugee camps. Additional sequenced isolates collected from two patients showed co-colonization with non-toxigenic C. diphtheriae biovar gravis, one of which exhibited decreased susceptibility to the first-line antibiotics and harboured a novel 23-kb multidrug resistance plasmid. Results of phylogenetic reconstruction and virulence-related gene contents of the recovered NDC isolates indicated they were likely commensal organisms, though 80.4 %(45/56) were not susceptible to erythromycin, and most showed high minimum inhibition concentrations against azithromycin. These results demonstrate the high resolution with which WGS can aid molecular investigation of diphtheria outbreaks, through the quantification of bacterial genetic relatedness, as well as the detection of virulence factors and antibiotic resistance markers among case isolates.

Genomic epidemiology of nontoxigenic Corynebacterium diphtheriae from King County, Washington State, USA between July 2018 and May 2019

Between July 2018 and May 2019, Corynebacterium diphtheriae was isolated from eight patients with non-respiratory infections, seven of whom experienced homelessness and had stayed at shelters in King County, WA, USA. All isolates were microbiologically identified as nontoxigenic C. diphtheriae biovar mitis. Whole-genome sequencing confirmed that all case isolates were genetically related, associated with sequence type 445 and differing by fewer than 24 single-nucleotide polymorphisms (SNPs). Compared to publicly available C. diphtheriae genomic data, these WA isolates formed a discrete cluster with SNP variation consistent with previously reported outbreaks. Virulence-related gene content variation within the highly related WA cluster isolates was also observed. These results indicated that genome characterization can readily support epidemiology of nontoxigenic C. diphtheriae.

First-line antibiotic susceptibility pattern of toxigenic Corynebacterium diphtheriae in Indonesia

BACKGROUND

Diphtheria has been reported as an outbreak in some regions in Indonesia, most especially in East Java Province. Resistance to penicillin, erythromycin, and other antibiotics, single or multiple, has been reported in several studies. This study aims to evaluate the first-line antibiotic susceptibility pattern of toxigenic Corynebacterium diphtheriae isolates.

METHODS

This descriptive observational study was performed from August to November 2018. C. diphtheriae isolates were collected from diphtheria patients and carriers in East Java from 2012 to 2017 and kept at the Balai Besar Laboratorium Kesehatan Daerah Surabaya or the Public Health Laboratory of Surabaya. Sample selection was done by random cluster sampling. The sensitivity test by E-test®of the five antibiotics (penicillin, oxacillin, erythromycin, azithromycin, and clarithromycin) was done to determine the minimum inhibitory concentration (MIC). The Clinical and Laboratory Standards Institute M45A (2015) Corynebacterium spp. for penicillin and erythromycin was used as standard.

RESULTS

From 114 targeted isolates, 108 were viable and toxigenic. The E-test was performed on the viable isolates. The majority of the hosts were male (58.3%), with median (range) age of 6.5 (1-14) years. Half of the samples were from the 1 to 5-year-old age group. The isolates were acquired much more from patients (78.7%) than carriers (21.3%) and from pharyngeal swab (74.1%). Most of these isolates were from Madura Island (47.2%) and the northern and eastern parts of the province (horseshoe area). Mitis isolates were the major variant (76.9%). The susceptibility pattern of C. diphtheriae to erythromycin was better than that to penicillin. The E-test result for penicillin was 68.52% susceptible, 31.48% intermediate, and 0% resistant (MIC range, < 0.016 to 2 μg/L) and for erythromycin (MIC range, < 0.016 to > 256 μg/L) was 85.2% susceptible, 12% intermediate, and 2.8% resistant The MIC range for oxacillin was 1 to 96 μg/L, while for both azithromycin and clarithromycin were <  0.016 to > 256 μg/L.

CONCLUSION

The susceptibility rate of C. diphtheriae to erythromycin is higher than that to penicillin. The regular update of antibiotic selection to the national guidelines is recommended. The MIC reference standard to azithromycin and clarithromycin is also needed.

Diphtheria

Diphtheria is a potentially fatal infection mostly caused by toxigenic Corynebacterium diphtheriae strains and occasionally by toxigenic C. ulcerans and C. pseudotuberculosis strains. Diphtheria is generally an acute respiratory infection, characterized by the formation of a pseudomembrane in the throat, but cutaneous infections are possible. Systemic effects, such as myocarditis and neuropathy, which are associated with increased fatality risk, are due to diphtheria toxin, an exotoxin produced by the pathogen that inhibits protein synthesis and causes cell death. Clinical diagnosis is confirmed by the isolation and identification of the causative Corynebacterium spp., usually by bacterial culture followed by enzymatic and toxin detection tests. Diphtheria can be treated with the timely administration of diphtheria antitoxin and antimicrobial therapy. Although effective vaccines are available, this disease has the potential to re-emerge in countries where the recommended vaccination programmes are not sustained, and increasing proportions of adults are becoming susceptible to diphtheria. Thousands of diphtheria cases are still reported annually from several countries in Asia and Africa, along with many outbreaks. Changes in the epidemiology of diphtheria have been reported worldwide. The prevalence of toxigenic Corynebacterium spp. highlights the need for proper clinical and epidemiological investigations to quickly identify and treat affected individuals, along with public health measures to prevent and contain the spread of this disease.

Molecular epidemiology and antimicrobial susceptibility of outbreak-associated Corynebacterium diphtheriae in Thailand, 2012

Infections caused by Corynebacterium diphtheriae remain endemic in many countries. Since the implementation of the DTP (Diphtheria-Tetanus-Pertussis) vaccination program in 1977, only sporadic diphtheria cases have been reported in Thailand. In 2012, a diphtheria outbreak occurred in rural Thailand and 38 cases were reported, with the majority being adults (mean 22.1 years, range 5-72 years). The current study determined the genetic diversity of C. diphtheriae isolated from 83 individuals associated with either sporadic (n = 34) from 1994, 1996, 1997, 1998, 1999, 2000, 2012, and 2018, or 2012 outbreak (n = 49) diphtheria occurrences in Thailand. Antimicrobial susceptibility testing was performed on 41/83 isolates using broth microdilution. All sporadic (n = 27) and epidemic (n = 14) C. diphtheriae isolates (41/41; 100%) were susceptible to erythromycin (≤0.5 μg/ml), clindamycin (≤0.5 μg/ml), gentamicin (≤ 4 μg/ml), ciprofloxacin (≤1 μg/ml), and vancomycin (2 μg/ml), except tetracycline with a resistance rate of 34.1% (14/41 isolates). All isolates were intermediately resistant to penicillin (MIC range, 0.25-2 μg/ml). Multilocus sequence typing (MLST) revealed 17 sequence types (STs) among 83C. diphtheriae isolates. For the 2012 outbreak isolates, the predominant ST was ST243 (n = 34/49; 69.4%), followed by ST245 (n = 5/49; 10.2%) and ST244 (n = 4/49; 8.1%), whereas the main STs among the sporadic isolates were ST248 (n = 15/34; 44.1%), followed by ST209 (n = 7/34; 20.6%) and ST258 (n = 3/34; 8.8%). The ST243 outbreak strain was a single-locus variant of sporadic ST258. Phylogenetic analysis using concatenated sequences of 7 MLST genes from 17 STs revealed that ST243, ST248, and ST258 were located in the same cluster and ST243 appeared to have evolved from ST258, an endemic strain. This study highlights the importance of epidemiological surveillance together with characterization of C. diphtheriae strains to help inform the future control and prevention of diphtheria.