Corynebacterium diphtheriae: genome diversity, population structure and genotyping perspectives

Neutralizing anti-diphtheria toxin scFv produced by phage display

BACKGROUND

Diphtheria can be prevented by vaccination, but some epidemics occur in several places, and diphtheria's threat is considerable. Administration of diphtheria antitoxin (DAT) produced from hyperimmunized animals is the most common treatment. Recombinant human antibody fragments such as single-chain variable fragments (scFv) produced by phage display library may introduce an interesting approach to overcome the limitations of the traditional antibody therapy. In the present study, B cells of immunized volunteers were used to construct a human single-chain fragment (HuscFv) library.

MATERIALS AND METHODS

The library was constructed with the maximum combination of heavy and light chains. As an antigen, Diphtheria toxoid (DTd) was used in four-round phage bio-panning to select phage clones that display DTd bound HuscFv from the library. After panning, individual scFv clones were selected. Clones that were able to detect DTd in an initial screening assay were transferred to Escherichia coli HB2151 to express the scFvs and purification was followed by Ni metal ion affinity chromatography. Toxin neutralization test was performed on Vero cells. The reactivity of the soluble scFv with diphtheria toxin were done and affinity calculation based on Beatty method was calculated.

RESULTS

The size of the constructed scFv library was calculated to be 1.3 × 106 members. Following four rounds of selection, 40 antibody clones were isolated which showed positive reactivity with DTd in an ELISA assay. Five clones were able to neutralize DTd in Vero cell assay. These neutralizing clones were used for soluble expression and purification of scFv fragments. Some of these soluble scFv fragments show neutralizing activity ranging from 0.6 to 1.2 µg against twofold cytotoxic dose of diphtheria toxin. The affinity constant of the selected scFv antibody was determined almost 107 M-1.

CONCLUSION

This study describes the prosperous construction and isolation of scFv from the immune library, which specifically neutralizes diphtheria toxin. The HuscFv produced in this study can be a potential candidate to substitute the animal antibody for treating diphtheria and detecting toxins.

Diphtheria in Metro Manila, the Philippines 2006-2017: A Clinical, Molecular, and Spatial Characterization

BACKGROUND

Diphtheria is a vaccine-preventable disease that persists as a global health problem. An understanding of the pattern of disease is lacking in low- and middle-income countries such as the Philippines.

METHODS

We conducted a retrospective review of the clinical, microbiological, and epidemiological features of patients admitted with a clinical diagnosis of diphtheria to an infectious disease referral hospital in Metro Manila, the Philippines, between 2006 and 2017. Cases were mapped and the distribution was compared with population density. Corynebacterium diphtheriae isolates from between 2015 and 2017 were examined by multilocus sequence typing (MLST).

RESULTS

We studied 267 patients (range:12-54 cases/year) admitted between 2006 and 2017. The case fatality rate (CFR) was 43.8% (95% confidence interval, 37.8-50.0%). A higher number of cases and CFR was observed among children <10 years. Mortality was associated with a delayed admission to hospital and a lack of diphtheria antitoxin. Between 2015 and 2017 there were 42 laboratory-confirmed cases. We identified 6 multilocus sequence types (STs). ST-302 was the most common (17/34, 48.6%), followed by ST67 (7/34, 20%) and ST458 (5/34, 14%). Case mapping showed a wide distribution of diphtheria patients in Metro Manila. Higher case numbers were found in densely populated areas but with no apparent clustering of ST types.

CONCLUSIONS

Our analysis indicates that diphtheria remains endemic in Metro Manila and that the infection is frequently fatal in young children. Improved vaccine coverage and a sustainable supply of diphtheria antitoxin should be prioritized.

Whole Genome Sequencing for Surveillance of Diphtheria in Low Incidence Settings

Corynebacterium diphtheriae (C. diphtheriae) is a relatively rare pathogen in most Western countries. While toxin producing strains can cause pharyngeal diphtheria with potentially fatal outcomes, the more common presentation is wound infections. The diphtheria toxin is encoded on a prophage and can also be carried by Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. Currently, across Europe, infections are mainly diagnosed in travelers and refugees from regions where diphtheria is more endemic, patients from urban areas with poor hygiene, and intravenous drug users. About half of the cases are non-toxin producing isolates. Rapid identification of the bacterial pathogen and toxin production is a critical element of patient and outbreak management. Beside the immediate clinical management of the patient, public health agencies should be informed of toxigenic C. diphtheriae diagnoses as soon as possible. The collection of case-related epidemiological data from the patient is often challenging due to language barriers and social circumstances. However, information on patient contacts, vaccine status and travel/refugee route, where appropriate, is critical, and should be documented. In addition, isolates should be characterized using high resolution typing, in order to identify transmissions and outbreaks. In recent years, whole genome sequencing (WGS) has become the gold standard of high-resolution typing methods, allowing detailed investigations of pathogen transmissions. De-centralized sequencing strategies with redundancy in sequencing capacities, followed by data exchange may be a valuable future option, especially since WGS becomes more available and portable. In this context, the sharing of sequence data, using public available platforms, is essential. A close interaction between microbiology laboratories, treating physicians, refugee centers, social workers, and public health officials is a key element in successful management of suspected outbreaks. Analyzing bacterial isolates at reference centers may further help to provide more specialized microbiological techniques and to standardize information, but this is also more time consuming during an outbreak. Centralized communication strategies between public health agencies and laboratories helps considerably in establishing and coordinating effective surveillance and infection control. We review the current literature on high-resolution typing of C. diphtheriae and share our own experience with the coordination of a Swiss-German outbreak.

The Prophages of Citrobacter rodentium Represent a Conserved Family of Horizontally Acquired Mobile Genetic Elements Associated with Enteric Evolution towards Pathogenicity

Bacteriophages are obligate intracellular parasites of bacteria. Some bacteriophages can confer novel bacterial phenotypes, including pathogenicity, through horizontal gene transfer (HGT). The pathogenic bacterium Citrobacter rodentium infects mice using mechanisms similar to those employed by human gastrointestinal pathogens, making it an important model organism. Here, we examined the 10 prophages of C. rodentium, investigating their roles in its evolution toward virulence. We characterized ΦNP and ΦSM, two endogenous active temperate bacteriophages likely important for HGT. We showed that the 10 prophages encode predicted virulence factors and are conserved within other intestinal pathogens. Phylogenetic analysis suggested that they represent a conserved family of horizontally acquired enteric-bacterium-associated pathogenic determinants. Consequently, similar analysis of prophage elements in other pathogens might further understanding of their evolution and pathology.

Prophage-mediated horizontal gene transfer (HGT) plays a key role in the evolution of bacteria, enabling access to new environmental niches, including pathogenicity. Citrobacter rodentium is a host-adapted intestinal mouse pathogen and important model organism for attaching and effacing (A/E) pathogens, including the clinically significant enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC, respectively). Even though C. rodentium contains 10 prophage genomic regions, including an active temperate phage, ΦNP, little was known regarding the nature of C. rodentium prophages in the bacterium’s evolution toward pathogenicity. In this study, our characterization of ΦNP led to the discovery of a second, fully functional temperate phage, named ΦSM. We identify the bacterial host receptor for both phages as lipopolysaccharide (LPS). ΦNP and ΦSM are likely important mediators of HGT in C. rodentium. Bioinformatic analysis of the 10 prophage regions reveals cargo genes encoding known virulence factors, including several type III secretion system (T3SS) effectors. C. rodentium prophages are conserved across a wide range of pathogenic enteric bacteria, including EPEC and EHEC as well as pathogenic strains of Salmonella enterica, Shigella boydii, and Klebsiella pneumoniae. Phylogenetic analysis of core enteric backbone genes compared against prophage evolutionary models suggests that these prophages represent an important, conserved family of horizontally acquired enteric-bacterium-associated pathogenicity determinants. In addition to highlighting the transformative role of bacteriophage-mediated HGT in C. rodentium’s evolution toward pathogenicity, these data suggest that the examination of conserved families of prophages in other pathogenic bacteria and disease outbreaks might provide deeper evolutionary and pathological insights otherwise obscured by more classical analysis.

IMPORTANCE Bacteriophages are obligate intracellular parasites of bacteria. Some bacteriophages can confer novel bacterial phenotypes, including pathogenicity, through horizontal gene transfer (HGT). The pathogenic bacterium Citrobacter rodentium infects mice using mechanisms similar to those employed by human gastrointestinal pathogens, making it an important model organism. Here, we examined the 10 prophages of C. rodentium, investigating their roles in its evolution toward virulence. We characterized ΦNP and ΦSM, two endogenous active temperate bacteriophages likely important for HGT. We showed that the 10 prophages encode predicted virulence factors and are conserved within other intestinal pathogens. Phylogenetic analysis suggested that they represent a conserved family of horizontally acquired enteric-bacterium-associated pathogenic determinants. Consequently, similar analysis of prophage elements in other pathogens might further understanding of their evolution and pathology.

Genome-wide comparison of Corynebacterium diphtheriae isolates from Australia identifies differences in the Pan-genomes between respiratory and cutaneous strains

Background

Corynebacterium diphtheriae is the main etiological agent of diphtheria, a global disease causing life-threatening infections, particularly in infants and children. Vaccination with diphtheria toxoid protects against infection with potent toxin producing strains. However a growing number of apparently non-toxigenic but potentially invasive C. diphtheriae strains are identified in countries with low prevalence of diphtheria, raising key questions about genomic structures and population dynamics of the species. This study examined genomic diversity among 48 C. diphtheriae isolates collected in Australia over a 12-year period using whole genome sequencing. Phylogeny was determined using SNP-based mapping and genome wide analysis.

Results

C. diphtheriae sequence type (ST) 32, a non-toxigenic clone with evidence of enhanced virulence that has been also circulating in Europe, appears to be endemic in Australia. Isolates from temporospatially related patients displayed the same ST and similarity in their core genomes. The genome-wide analysis highlighted a role of pilins, adhesion factors and iron utilization in infections caused by non-toxigenic strains.

Conclusions

The genomic diversity of toxigenic and non-toxigenic strains of C. diphtheriae in Australia suggests multiple sources of infection and colonisation. Genomic surveillance of co-circulating toxigenic and non-toxigenic C. diphtheriae offer new insights into the evolution and virulence of pathogenic clones and can inform targeted public health actions and policy. The genomes presented in this investigation will contribute to the global surveillance of C. diphtheriae both for the monitoring of antibiotic resistance genes and virulent strains such as those belonging to ST32.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5147-2) contains supplementary material, which is available to authorized users.

Identification of novel lipid modifications and intermembrane dynamics in Corynebacterium glutamicum using high-resolution mass spectrometry

The complex cell envelopes of Corynebacterineae contribute to the virulence of pathogenic species (such as Mycobacterium tuberculosis and Corynebacterium diphtheriae) and capacity of nonpathogenic species (such as Corynebacterium glutamicum) to grow in diverse niches. The Corynebacterineae cell envelope comprises an asymmetric outer membrane that overlays the arabinogalactan-peptidoglycan complex and the inner cell membrane. Dissection of the lipid composition of the inner and outer membrane fractions is important for understanding the biogenesis of this multilaminate wall structure. Here, we have undertaken the first high-resolution analysis of C. glutamicum inner and outer membrane lipids. We identified 28 lipid (sub)classes (>233 molecular species), including new subclasses of acylated/acetylated trehalose mono/dicorynomycolic acids, using high-resolution LC/MS/MS coupled with mass spectral library searches in MS-DIAL. All lipid subclasses exhibited polarized distributions across the inner and outer membrane fractions generated by differential solvent extraction. Strikingly, deletion of the TmaT protein, which is required for transport of trehalose corynomycolates across the inner membrane, led to the accumulation of triacylglycerols in the inner membrane and to suppressed synthesis of phosphatidylglycerol and alanylated lipids. These analyses indicate unanticipated connectivity in the synthesis and/or transport of different lipid classes in C. glutamicum.

Diagnosis in France of a Non-Toxigenic tox Gene-Bearing Strain of Corynebacterium diphtheriae in a Young Male Back From Senegal

Cutaneous diphtheria is uncommon in Europe. In this study, we report a case of imported cutaneous infection due to a non-toxigenic but tox gene-bearing (NTTB) strain of Corynebacterium diphtheriae. The NTTB strains are recognized as emerging pathogens across Europe, and physicians and bacteriologists should be aware of the circulation of these strains.

Outbreak investigation for toxigenic Corynebacterium diphtheriae wound infections in refugees from Northeast Africa and Syria in Switzerland and Germany by whole genome sequencing

Toxigenic Corynebacterium diphtheriae is an important and potentially fatal threat to patients and public health. During the current dramatic influx of refugees into Europe, our objective was to use whole genome sequencing for the characterization of a suspected outbreak of C. diphtheriae wound infections among refugees. After conventional culture, we identified C. diphtheriae using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and investigated toxigenicity by PCR. Whole genome sequencing was performed on a MiSeq Illumina with >70×coverage, 2×250 bp read length, and mapping against a reference genome. Twenty cases of cutaneous C. diphtheriae in refugees from East African countries and Syria identified between April and August 2015 were included. Patients presented with wound infections shortly after arrival in Switzerland and Germany. Toxin production was detected in 9/20 (45%) isolates. Whole genome sequencing-based typing revealed relatedness between isolates using neighbour-joining algorithms. We detected three separate clusters among epidemiologically related refugees. Although the isolates within a cluster showed strong relatedness, isolates differed by >50 nucleotide polymorphisms. Toxigenic C. diphtheriae associated wound infections are currently observed more frequently in Europe, due to refugees travelling under poor hygienic conditions. Close genetic relatedness of C. diphtheriae isolates from 20 refugees with wound infections indicates likely transmission between patients. However, the diversity within each cluster and phylogenetic time-tree analysis suggest that transmissions happened several months ago, most likely outside Europe. Whole genome sequencing offers the potential to describe outbreaks at very high resolution and is a helpful tool in infection tracking and identification of transmission routes.

Microbiological and molecular characterization of Corynebacterium diphtheriae isolated in Algeria between 1992 and 2015

The objectives of this study were to undertake the microbiological and molecular characterization of Corynebacterium diphtheriae isolates collected in Algeria during epidemic and post-epidemic periods between 1992 and 2015. Microbiological characterization includes the determination of biotype and toxigenicity status using phenotypic and genotypic methods. Antimicrobial susceptibility was determined by the E-test method. Molecular characterization was performed by multi-locus sequence typing. In total, there were 157 cases of C. diphtheriae isolates, 127 in patients with respiratory diphtheria and 30 with ozena. Isolates with a mitis biotype were predominant (122 out of 157; 77.7%) followed by belfanti (28 out of 157; 17.8%) and gravis biotype (seven out of 157; 4.5%). Toxigenic isolates were predominant in the period 1992-2006 (74 out of 134) whereas in the period 2007-2015, only non-toxigenic isolates circulated (23 out of 23). All 157 isolates were susceptible to erythromycin, gentamicin, vancomycin and cotrimoxazole. Reduced susceptibility to penicillin G, cefotaxime, tetracycline and chloramphenicol was detected in 90 (57.3%), 88 (56.1%), 112 (71.3%) and 90 (57.3%) isolates, respectively. Multi-locus sequence typing analysis indicates that sequence type 116 (ST-116) was the most frequent, with 65 out of 100 isolates analysed, in particular during the epidemic period 1992-1999 (57 out of 65 isolates). In the post-epidemic period, 2000-2015, 13 different sequence types were isolated. All belfanti isolates (ten out of 100 isolates) belonged to closely related sequence types grouped in a phylogenetically distinct eBurst group and were collected exclusively in ozena cases. In conclusion, the epidemic period was associated with ST-116 while the post-epidemic period was characterized by more diversity. Belfanti isolates are grouped in a phylogenetically distinct clonal complex.

The ChrSA and HrrSA Two-Component Systems Are Required for Transcriptional Regulation of the hemA Promoter in Corynebacterium diphtheriae

Corynebacterium diphtheriae utilizes heme and hemoglobin (Hb) as iron sources for growth in low-iron environments. In C. diphtheriae, the two-component signal transduction systems (TCSs) ChrSA and HrrSA are responsive to Hb levels and regulate the transcription of promoters for hmuO, hrtAB, and hemA ChrSA and HrrSA activate transcription at the hmuO promoter and repress transcription at hemA in an Hb-dependent manner. In this study, we show that HrrSA is the predominant repressor at hemA and that its activity results in transcriptional repression in the presence and absence of Hb, whereas repression of hemA by ChrSA is primarily responsive to Hb. DNA binding studies showed that both ChrA and HrrA bind to the hemA promoter region at virtually identical sequences. ChrA binding was enhanced by phosphorylation, while binding to DNA by HrrA was independent of its phosphorylation state. ChrA and HrrA are phosphorylated in vitro by the sensor kinase ChrS, whereas no kinase activity was observed with HrrS in vitro Phosphorylated ChrA was not observed in vivo, even in the presence of Hb, which is likely due to the instability of the phosphate moiety on ChrA. However, phosphorylation of HrrA was observed in vivo regardless of the presence of the Hb inducer, and genetic analysis indicates that ChrS is responsible for most of the phosphorylation of HrrA in vivo Phosphorylation studies strongly suggest that HrrS functions primarily as a phosphatase and has only minimal kinase activity. These findings collectively show a complex mechanism of regulation at the hemA promoter, where both two-component systems act in concert to optimize expression of heme biosynthetic enzymes.

IMPORTANCE

Understanding the mechanism by which two-component signal transduction systems function to respond to environmental stimuli is critical to the study of bacterial pathogenesis. The current study expands on the previous analyses of the ChrSA and HrrSA TCSs in the human pathogen C. diphtheriae The findings here underscore the complex interactions between the ChrSA and HrrSA systems in the regulation of the hemA promoter and demonstrate how the two systems complement one another to refine and control transcription in the presence and absence of Hb.

Genomic analysis of a nontoxigenic, invasive Corynebacterium diphtheriae strain from Brazil

We report the complete genome sequence and analysis of an invasive Corynebacterium diphtheriae strain that caused endocarditis in Rio de Janeiro, Brazil. It was selected for sequencing on the basis of the current relevance of nontoxigenic strains for public health. The genomic information was explored in the context of diversity, plasticity and genetic relatedness with other contemporary strains.

Corynebacterium ulcerans cutaneous diphtheria

We describe the case of a patient with cutaneous diphtheria caused by toxigenic Corynebacterium ulcerans who developed a right hand flexor sheath infection and symptoms of sepsis such as fever, tachycardia, and elevated C-reactive protein, after contact with domestic cats and dogs, and a fox. We summarise the epidemiology, clinical presentation, microbiology, diagnosis, therapy, and public health aspects of this disease, with emphasis on improving recognition. In many European countries, C ulcerans has become the organism commonly associated with cutaneous diphtheria, usually seen as an imported tropical disease or resulting from contact with domestic and agricultural animals. Diagnosis relies on bacterial culture and confirmation of toxin production, with management requiring appropriate antimicrobial therapy and prompt administration of antitoxin, if necessary. Early diagnosis is essential for implementation of control measures and clear guidelines are needed to assist clinicians in managing clinical diphtheria. This case was a catalyst to the redrafting of the 2014 national UK interim guidelines for the public health management of diphtheria, released as final guidelines in March, 2015.

Emerging methods to study bacteriophage infection at the single-cell level

Bacteria and their viruses (phages) are abundant across diverse ecosystems and their interactions influence global biogeochemical cycles and incidence of disease. Problematically, both classical and metagenomic methods insufficiently assess the host specificity of phages and phage–host infection dynamics in nature. Here we review emerging methods to study phage–host interaction and infection dynamics with a focus on those that offer resolution at the single-cell level. These methods leverage ever-increasing sequence data to identify virus signals from single-cell amplified genome datasets or to produce primers/probes to target particular phage–bacteria pairs (digital PCR and phageFISH), even in complex communities. All three methods enable study of phage infection of uncultured bacteria from environmental samples, while the latter also discriminates between phage–host interaction outcomes (e.g., lytic, chronic, lysogenic) in model systems. Together these techniques enable quantitative, spatiotemporal studies of phage–bacteria interactions from environmental samples of any ecosystem, which will help elucidate and predict the ecological and evolutionary impacts of specific phage–host pairings in nature.

Structure of a DsbF homologue from Corynebacterium diphtheriae

Disulfide-bond formation, mediated by the Dsb family of proteins, is important in the correct folding of secreted or extracellular proteins in bacteria. In Gram-negative bacteria, disulfide bonds are introduced into the folding proteins in the periplasm by DsbA. DsbE from Escherichia coli has been implicated in the reduction of disulfide bonds in the maturation of cytochrome c. The Gram-positive bacterium Mycobacterium tuberculosis encodes DsbE and its homologue DsbF, the structures of which have been determined. However, the two mycobacterial proteins are able to oxidatively fold a protein in vitro, unlike DsbE from E. coli. In this study, the crystal structure of a DsbE or DsbF homologue protein from Corynebacterium diphtheriae has been determined, which revealed a thioredoxin-like domain with a typical CXXC active site. Structural comparison with M. tuberculosis DsbF would help in understanding the function of the C. diphtheriae protein.

σ(ECF) factors of gram-positive bacteria: a focus on Bacillus subtilis and the CMNR group

The survival of bacteria to different environmental conditions depends on the activation of adaptive mechanisms, which are intricately driven through gene regulation. Because transcriptional initiation is considered to be the major step in the control of bacterial genes, we discuss the characteristics and roles of the sigma factors, addressing (1) their structural, functional and phylogenetic classification; (2) how their activity is regulated; and (3) the promoters recognized by these factors. Finally, we focus on a specific group of alternative sigma factors, the so-called σ(ECF) factors, in Bacillus subtilis and some of the main species that comprise the CMNR group, providing information on the roles they play in the microorganisms' physiology and indicating some of the genes whose transcription they regulate.

The utility of the PCR melting profile technique for typing Corynebacterium diphtheriae isolates

Selection of appropriate typing method depends on a number of factors, including the scale of the investigation, the rapidity required of the results and the financial and technical resources available. Several typing methods have been applied to Corynebacterium diphtheriae genotyping, but most are laborious and time-consuming or require expensive equipment. We report an evaluation of the utility of the PCR melting profile technique for simple and easy-to-perform genotyping of C. diphtheriae. We compared the method with ribotyping-the 'gold standard' for C. diphtheriae typing-and PFGE, MLST, AFLP, RAPD and spoligotyping.

SIGNIFICANCE AND IMPACT OF THE STUDY

Occurrence of Corynebacterium diphtheriae infections-in the form of diphtheria in endemic countries and in the form of invasive infections in countries with high antidiphtheria vaccination coverage-indicates the need for maintenance of ability to genotype this pathogen by laboratories. Application of an appropriate typing method is essential not only in outbreak investigations for understanding and predicting epidemics but also in monitoring of the evolution and spread of epidemic clones of C. diphtheriae. The PCR melting profile method presented in the study is a good alternative for C. diphtheriae typing.

Microbiological changes and diversity in autochthonous non-toxigenic Corynebacterium diphtheriae isolated in France

Autochtonous toxigenic Corynebacterium diphtheriae have disappeared in mainland France, but non-toxigenic C. diphtheriae are still circulating. Using phenotypic and molecular tools, we retrospectively characterized 103 non-toxigenic C. diphtheriae collected in mainland France and highlight several changes. The proportion of C. diphtheriae belfanti increased between 1977 and 2011 and it is the most frequent biotype recovered in recent years. Resistance to ciprofloxacin has increased and most isolates with decreased sensitivity belong to the belfanti biotype. Using multilocus sequence typing, we demonstrate that French isolates are distributed in a large number of sequence types and identify three distinct lineages. C. diphtheriae mitis and gravis form lineage I while C. diphtheriae belfanti forms lineages II and III. Almost all isolates of lineage II are part of a unique clonal complex or are very close to it. Most French isolates have a dtxR sequence homologous to that of toxigenic isolates, suggesting that if lyzogenised by a corynephage, they can express diphtheria toxin.

The ChrA response regulator in Corynebacterium diphtheriae controls hemin-regulated gene expression through binding to the hmuO and hrtAB promoter regions

Corynebacterium diphtheriae, the etiologic agent of diphtheria, utilizes heme and hemoglobin (Hb) as iron sources for growth. Heme-iron utilization involves HmuO, a heme oxygenase that degrades cytosolic heme, resulting in the release of heme-associated iron. Expression of the hmuO promoter is under dual regulation, in which transcription is repressed by DtxR and iron and activated by a heme source, such as hemin or Hb. Hemin-dependent activation is mediated primarily by the ChrAS two-component system, in which ChrS is a putative heme-responsive sensor kinase while ChrA is proposed to serve as a response regulator that activates transcription. It was recently shown that the ChrAS system similarly regulates the hrtAB genes, which encode an ABC transporter involved in the protection of C. diphtheriae from hemin toxicity. In this study, we characterized the phosphorelay mechanism in the ChrAS system and provide evidence for the direct regulation of the hmuO and hrtAB promoters by ChrA. A fluorescence staining method was used to show that ChrS undergoes autophosphorylation and that the phosphate moiety is subsequently transferred to ChrA. Promoter fusion studies identified regions upstream of the hmuO and hrtAB promoters that are critical for the heme-dependent regulation by ChrA. Electrophoretic mobility shift assays revealed that ChrA specifically binds at the hmuO and hrtAB promoter regions and that binding is phosphorylation dependent. A phosphorylation-defective mutant of ChrA [ChrA(D50A)] exhibited significantly diminished binding to the hmuO promoter region relative to that of wild-type ChrA. DNase I footprint analysis further defined the sequences in the hmuO and hrtAB promoters that are involved in ChrA binding, and this analysis revealed that the DtxR binding site at the hmuO promoter partially overlaps the binding site for ChrA. DNase I protection studies as well as promoter fusion analysis suggest that ChrA and DtxR compete for binding at the hmuO promoter. Collectively, these data demonstrate that the ChrA response regulator directly controls the expression of hmuO and the hrtAB genes and the binding activity of ChrA is dependent on phosphorylation by its cognate sensor kinase ChrS.

Cutaneous diphtheria in the urban poor population of Vancouver, British Columbia, Canada: a 10-year review

Between 1998 and 2007, records from 33 patients with cutaneous diphtheria from Vancouver's inner city were reviewed. Cases were associated with injection drug use and poverty. Coinfections with Staphylococcus aureus, Streptococcus pyogenes, and Arcanobacterium haemolyticum occurred. Corynebacterium diphtheriae is endemic in Vancouver's urban core, with strains of multilocus sequence type (MLST) 76 predominating.

The rise and fall of the Mycobacterium tuberculosis genome

When studied from the perspective of non-tuberculous mycobacteria (NTM) it is apparent that Mycobacterium tuberculosis has undergone a biphasic evolutionary process involving genome expansion (gene acquisition and duplication) and reductive evolution (deletions). This scheme can instruct descriptive and experimental studies that determine the importance of ancestral events (including horizontal gene transfer) in shaping the present-day pathogen. For example, heterologous complementation in an NTM can test the functional importance of M. tuberculosis-specific genetic insertions. An appreciation of both phases of M. tuberculosis evolution is expected to improve our fundamental understanding of its pathogenicity and facilitate the evaluation of novel diagnostics and vaccines.

Identification of Corynebacterium diphtheriae gene involved in adherence to epithelial cells

Corynebacterium diphtheriae the causative pathogen of human diphtheria infects the nasopharynx or skin. Although diphtheria has been extensively studied, little is known about the two key aspects of C. diphtheriae invasiveness: colonization and invasion. The role of adhesive properties in establishing the infection of C. diphtheriae strains, independent of toxin production, still needs to be clarified. In this study, we describe a novel gene involved in adherence to epithelial cells. Transformation of C. diphtheriae 225, biotype gravis, ribotype St-Petersburg by EZ:TN(KAN-2)Tnp Transposome was undertaken. A C. diphtheriae 225 Tn5 insertion library of 2800 mutants was created. Five hundred and eighty five transformants were qualitatively screened for reduced adherence to HEp-2 cells by an adherence assay. One mutant strain consistently exhibiting 15.2% of the wild-type adherence was isolated. The DNA flanking the transposon was identified by inverse PCR and subsequent sequencing. The disrupted gene was 94% identical to the C. diphtheriae DIP1621 gene that belongs to unclassified genes. In conclusion, the disruption of the C. diphtheriae DIP1621 gene led to decreased adherence to epithelial cells; its exact function remains to be established.

International external quality assurance for laboratory diagnosis of diphtheria

The diphtheria surveillance network (DIPNET) encompassing National Diphtheria Reference Centers from 25 European countries is a Dedicated Surveillance Network recognized by the European Commission. A key DIPNET objective is the quality assessment of microbiological procedures for diphtheria across the European Union and beyond. A detailed questionnaire on the level of reference laboratory services and an external quality assessment (EQA) panel comprising six simulated throat specimens were sent to 34 centers. Twenty-three centers are designated National Diphtheria Reference Centers, with the laboratory in the United Kingdom being the only WHO Collaborating Centre. A variety of screening and identification tests were used, including the cysteinase test (20/34 centers), pyrazinamidase test (17/34 centers), and commercial kits (25/34 centers). The classic Elek test for toxigenicity testing is mostly used (28/34 centers), with variations in serum sources and antitoxin concentrations. Many laboratories reported problems obtaining Elek reagents or media. Only six centers produced acceptable results for all six specimens. Overall, 21% of identification and 13% of toxigenicity reports were unacceptable. Many centers could not isolate the target organism, and most found difficulties with the specimens that contained Corynebacterium striatum as a commensal contaminant. Nineteen centers generated either false-positive or negative toxigenic results, which may have caused inappropriate medical management. The discrepancies in this diphtheria diagnostics EQA alarmingly reflect the urgent need to improve laboratory performance in diphtheria diagnostics in Europe, standardize feasible and robust microbiological methods, and build awareness among public health authorities. Therefore, DIPNET recommends that regular workshops and EQA distributions for diphtheria diagnostics should be supported and maintained.