Polymerase chain reaction assay for diagnosis of potentially toxinogenic Corynebacterium diphtheriae strains: correlation with ADP-ribosylation activity assay

Challenges of Diphtheria Toxin Detection

Diphtheria toxin (DT) is the main virulence factor of Corynebacterium diphtheriae, C. ulcerans and C. pseudotuberculosis. Moreover, new Corynebacterium species with the potential to produce diphtheria toxin have also been described. Therefore, the detection of the toxin is the most important test in the microbiological diagnosis of diphtheria and other corynebacteria infections. Since the first demonstration in 1888 that DT is a major virulence factor of C. diphtheriae, responsible for the systemic manifestation of the disease, various methods for DT detection have been developed, but the diagnostic usefulness of most of them has not been confirmed on a sufficiently large group of samples. Despite substantial progress in the science and diagnostics of infectious diseases, the Elek test is still the basic recommended diagnostic test for DT detection. The challenge here is the poor availability of an antitoxin and declining experience even in reference laboratories due to the low prevalence of diphtheria in developed countries. However, recent and very promising assays have been developed with the potential for use as rapid point-of-care testing (POCT), such as ICS and LFIA for toxin detection, LAMP for tox gene detection, and biosensors for both.

Outbreak of Corynebacterium diphtheriae among asylum seekers in Belgium in 2022: operational challenges and lessons learnt

Since 2022, European countries have been facing an outbreak of mainly cutaneous diphtheria caused by toxigenic Corynebacterium diphtheriae among asylum seekers. In Belgium, between 1 March and 31 December 2022, 25 cases of toxigenic C. diphtheriae infection were confirmed among asylum seekers, mostly among young males from Afghanistan. Multi-locus sequence typing showed that most isolates belonged to sequence types 574 or 377, similar to the majority of cases in other European countries. The investigation and management of the outbreak, with many asylum seekers without shelter, required adjustments to case finding, contact tracing and treatment procedures. A test-and-treat centre was organised by non-governmental organisations, the duration of the antimicrobial treatment was shortened to increase compliance, and isolation and contact tracing of cases was not possible. A vaccination centre was opened, and mobile vaccination campaigns were organised to vaccinate a maximum of asylum seekers. No more cases were detected between end December 2022 and May 2023. Unfortunately, though, three cases of respiratory diphtheria, including one death, were reported at the end of June 2023. To prevent future outbreaks, specific attention and sufficient resources should be allocated to this vulnerable population, in Belgium and at international level.

Genomic Analysis of Corynebacterium diphtheriae Strains Isolated in the Years 2007-2022 with a Report on the Identification of the First Non-Toxigenic tox Gene-Bearing Strain in Poland

Infections caused by non-toxigenic Corynebacterium diphtheriae have been reported every year in Poland since 2004, with the ST8 biovar gravis strains being most commonly isolated. This study analyzed thirty strains isolated between 2017 and 2022 and six previously isolated strains. All the strains were characterized using classic methods in terms of species, biovar level, and diphtheria toxin production, as well as by means of whole genome sequencing. The phylogenetic relationship based on SNP analysis was determined. The number of C. diphtheriae infections has been rising in Poland every year with a maximum of 22 cases in the year 2019. Since 2022, only the non-toxigenic gravis ST8 (most common) and mitis ST439 (less common) strains have been isolated. An analysis of the genomes of the ST8 strains showed that they had many potential virulence factors, such as adhesins and iron-uptake systems. The situation rapidly changed in 2022 and strains from different STs were isolated (ST32, 40, and 819). The ST40 biovar mitis strain was found to be non-toxigenic tox gene-bearing (NTTB), with the tox gene inactivated due to a single nucleotide deletion. Such strains were previously isolated in Belarus. The sudden appearance of new C. diphtheriae strains with different STs and the isolation of the first NTTB strain in Poland indicate that C. diphtheriae should be classified as a pathogen of special public health concern.

Application of Polymerase Chain Reaction in Diphtheria Laboratory Examination: A Field Need

Background: Indonesia is one of the five countries with the highest number of diphtheria cases worldwide. Diphtheria is caused by the toxigenic strains Corynebacterium diphtheriae, C. ulcerans, and C. pseudotuberculosis. The diphtheria-causing bacteria can be identified using conventional and molecular methods, including polymerase chain reaction (PCR) assay. We used the PCR assay as additional testing, because in island countries like Indonesia, specimen transport is a serious challenge to maintaining bacterial survival. Objectives: This study aimed to evaluate the PCR assay as additional testing to identify diphtheria-causing bacteria in the diphtheria laboratory. Methods: In this cross-sectional study, a total of 178 pairs of the throat and nasal swabs from diphtheria suspected cases and close contacts were collected from seven provinces in Indonesia in 2016. All samples were directly identified by the conventional method and multiplex PCR assay. Statistical analysis was conducted using the 2 × 2 tables to determine the sensitivity and specificity of both methods, while the χ2 test was used to examine the correlation between specimen examination delay and the differentiation of results. A P-value < 0.05 was considered as statistically significant. Results: Out of 178 examined samples, eight samples were identified as diphtheria-positive by both the conventional method and PCR assay, while nine samples were only detected by the PCR assay. All diphtheria-causing bacteria found in the positive samples were toxigenic C. diphtheriae. The diphtheria-causing bacteria were found in 27.6% of cases and 6.0% of close contacts using the PCR assay versus 13.8% of cases and 2.7% of close contacts using the conventional method. Statistical analysis showed that the PCR assay is about twice more sensitive than the conventional method. There was a significant correlation between the differentiation of results and > 72 hours’ specimen examination delay with a P-value of 0.04 (< 0.05). Conclusions: The PCR assay is more sensitive than the conventional method to identify diphtheria-causing bacteria and may be applied as additional testing to increase the positivity rate of diphtheria-confirmed cases in Indonesia as an archipelago country where geographical factors and specimen transport are real obstacles.

Detection of toxin-producing Corynebacterium diphtheriae from throat swabs of diphtheria patients using duplex real-time PCR

Background and Objectives

Diphtheria is a potentially fatal disease caused by toxigenic bacterial infection, particularly from Corynebacterium diphtheriae (C. diphtheriae). Isolation of C. diphtheriae is technically lacking in sensitivity, and Elek's test to detect toxin production has several difficulties associated with its application. Duplex real-time PCR to throat swab of suspected diphtheria patients can detect both bacteria and toxin-encoding genes simultaneously, faster, with higher sensitivity and specificity.

Materials and Methods

A total of 89 consecutive throat swabs from suspected diphtheria patients were collected from Sulianti Saroso Infectious Disease Hospital, Jakarta, during 2018 to 2019. Two pairs of primers and probes, targeting the rpoB gene of C. diphtheriae and the A-subunit of the diphtheria toxin gene, were used in this study. Parameters including annealing temperature, concentration of primers and probes, inhibitors, cross-reaction and detection limit were all optimized. Elek's toxigenicity test and clinical data were analyzed for comparison.

Results

The optimum annealing temperature was 55°C. The concentrations of Cd primer, Tox primer, Cd probe and Tox probe were 0.4, 0.6, 0.5 and 0.625 µM, respectively. DNA elution and template volumes were 50 µL and 5 µL. The detection limit was 2 CFU/mL. No cross-reaction with other microorganisms was observed. Of the 89 samples, duplex real-time PCR gave better results than the standard test, with 19 (21.3%) and 10 (11.2%) patients diagnosed with diphtheria, respectively.

Conclusion

Duplex real-time PCR increases the rate of laboratory diagnosis of diphtheria, compared to the standard method to detect potentially toxigenic C. diphtheriae.

Population genomics and antimicrobial resistance in Corynebacterium diphtheriae

Background

Corynebacterium diphtheriae, the agent of diphtheria, is a genetically diverse bacterial species. Although antimicrobial resistance has emerged against several drugs including first-line penicillin, the genomic determinants and population dynamics of resistance are largely unknown for this neglected human pathogen.

Methods

Here, we analyzed the associations of antimicrobial susceptibility phenotypes, diphtheria toxin production, and genomic features in C. diphtheriae. We used 247 strains collected over several decades in multiple world regions, including the 163 clinical isolates collected prospectively from 2008 to 2017 in France mainland and overseas territories.

Results

Phylogenetic analysis revealed multiple deep-branching sublineages, grouped into a Mitis lineage strongly associated with diphtheria toxin production and a largely toxin gene-negative Gravis lineage with few toxin-producing isolates including the 1990s ex-Soviet Union outbreak strain. The distribution of susceptibility phenotypes allowed proposing ecological cutoffs for most of the 19 agents tested, thereby defining acquired antimicrobial resistance. Penicillin resistance was found in 17.2% of prospective isolates. Seventeen (10.4%) prospective isolates were multidrug-resistant (≥ 3 antimicrobial categories), including four isolates resistant to penicillin and macrolides. Homologous recombination was frequent (r/m = 5), and horizontal gene transfer contributed to the emergence of antimicrobial resistance in multiple sublineages. Genome-wide association mapping uncovered genetic factors of resistance, including an accessory penicillin-binding protein (PBP2m) located in diverse genomic contexts. Gene pbp2m is widespread in other Corynebacterium species, and its expression in C. glutamicum demonstrated its effect against several beta-lactams. A novel 73-kb C. diphtheriae multiresistance plasmid was discovered.

Conclusions

This work uncovers the dynamics of antimicrobial resistance in C. diphtheriae in the context of phylogenetic structure, biovar, and diphtheria toxin production and provides a blueprint to analyze re-emerging diphtheria.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13073-020-00805-7.

Corynebacterium rouxii sp. nov., a novel member of the diphtheriae species complex

A group of six clinical isolates previously identified as Corynebacterium diphtheriae biovar Belfanti, isolated from human cutaneous or peritoneum infections and from one dog, were characterized by genomic sequencing, biochemical analysis and MALDI-TOF mass spectrometry. The six isolates were negative for the diphtheria toxin gene. Phylogenetic analyses showed that the six isolates (including FRC0190^T) are clearly demarcated from C. diphtheriae, Corynebacterium belfantii, Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. The average nucleotide identity of FRC0190^T with C. diphtheriae NCTC11397^T was 92.6%, and was 91.8% with C. belfantii FRC0043^T. C. diphtheriae subsp. lausannense strain CHUV2995^T appeared to be a later heterotypic synonym of C. belfantii (ANI, 99.3%). Phenotyping data revealed an atypical negative or heterogeneous intermediate maltose fermentation reaction for the six isolates. MALDI-TOF mass spectrometry differentiated the new group from the other Corynebacterium taxa by the presence of specific spectral peaks. rpoB sequences showed identity to atypical, maltose-negative C. diphtheriae biovar Belfanti isolates previously described from two cats in the USA. We propose the name Corynebacterium rouxii sp. nov. for the novel group, with FRC0190^T (= CIP 111752^T = DSM 110354^T) as type strain.

Diphtheria in Belgium: 2010-2017

In Western Europe, the incidence of both respiratory and cutaneous diphtheria, caused by toxin-producing Corynebacterium diphtheriae, Corynebacterium ulcerans or Corynebacterium pseudotuberculosis, has been low over the past few decades thanks to the use of an effective vaccine and a high level of vaccination coverage. However, the disease has still not been eradicated and continues to occur in all of Europe. In order to prevent sequelae or a fatal outcome, diphtheria antitoxin (DAT) should be administered to suspected diphtheria patients as soon as possible, but economic factors and issues concerning regulations have led to poor availability of DAT in many countries. The European Centre for Disease Prevention and Control and World Health Organization have called for European Union-wide solutions to this DAT-shortage. In order to illustrate the importance of these efforts and underline the need for continued diphtheria surveillance, we present data on all registered cases of toxigenic and non-toxigenic C. diphtheriae, C. ulcerans and C. pseudotuberculosis in Belgium during the past decade, up to and including 2017.

Re-emergence of Corynebacterium diphtheriae

BACKGROUND

Diphtheria is re-emerging in Europe. A total of 36 cases were reported in Europe in 2015 versus 53 cases between 2000 and 2009.

PATIENTS

We report two cases of Corynebacterium diphtheriae infection in a French hospital in 2016: a cutaneous infection with negative toxin testing in a French traveller, and a respiratory diphtheria carriage with positive toxin testing in an Afghan refugee diagnosed with pulmonary tuberculosis. The vaccination history of the Afghan patient could not be retrieved.

Taxonomic status of Corynebacterium diphtheriae biovar Belfanti and proposal of Corynebacterium belfantii sp. nov

Clinical isolates belonging to Corynebacterium diphtheriae biovar Belfanti were characterized by genomic sequencing and biochemical and chemotaxonomic analyses. Phylogenetic analyses indicated that biovar Belfanti represents a branch that is clearly demarcated from C. diphtheriae strains of biovars Mitis and Gravis. The average nucleotide identity of isolates of biovar Belfanti with C. diphtheriae type strain NCTC 11397^T (biovar Gravis) was 94.85 %. The inability to reduce nitrate differentiated biovar Belfanti from other strains of C. diphtheriae. On the basis of these results, we propose the name Corynebacterium belfantii sp. nov. for the group of strains previously considered as C. diphtheriaebiovar Belfanti. The type strain of C. belfantii is FRC0043^T (=CIP 111412^T=DSM 105776^T). Strains of C. belfantii were isolated mostly from human respiratory samples.

Contemporary microbiology and identification of Corynebacteria spp. causing infections in human

The Corynebacterium is a genus of bacteria of growing clinical importance. Progress in medicine results in growing population of immunocompromised patients and growing number of infections caused by opportunistic pathogens. A new infections caused by new Corynebacterium species and species previously regarded as commensal micro-organisms have been described. Parallel with changes in Corynebacteria infections, the microbiological laboratory diagnostic possibilities are changing. But identification of this group of bacteria to the species level remains difficult. In the paper, we present various manual, semi-automated and automated assays used in clinical laboratories for Corynebacterium identification, such as API Coryne, RapID CB Plus, BBL Crystal Gram Positive ID System, MICRONAUT-RPO, VITEK 2, BD Phoenix System, Sherlock Microbial ID System, MicroSeq Microbial Identification System, Biolog Microbial Identification Systems, MALDI-TOF MS systems, polymerase chain reaction (PCR)-based and sequencing-based assays. The presented assays are based on various properties, like biochemical tests, specific DNA sequences, composition of cellular fatty acids, protein profiles and have specific limitations.

SIGNIFICANCE AND IMPACT OF THE STUDY

The number of opportunistic infections caused by Corynebacteria is increasing due to increase in number of immunocompromised patients. New Corynebacterium species and new human infections, caused by this group of bacteria, has been described recently. However, identification of Corynebacteria is still a challenge despite application of sophisticated laboratory methods. In the study we present possibilities and limitations of various commercial systems for identification of Corynebacteria.

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.

Outbreak with clonally related isolates of Corynebacterium ulcerans in a group of water rats

Background

The zoonotic bacterium Corynebacterium ulcerans may be pathogenic both in humans and animals: toxigenic strains can cause diphtheria or diphtheria-like disease in humans via diphtheria toxin, while strains producing the dermonecrotic exotoxin phospholipase D may lead to caseous lymphadenitis primarily in wild animals. Diphtheria toxin-positive Corynebacterium ulcerans strains have been isolated mainly from cattle, dogs and cats.

Results

Here, we report a series of ten isolations of Corynebacterium ulcerans from a group of water rats (Hydromys chrysogaster) with ulcerative skin lesions, which were kept in a zoo. The isolates were clearly assigned to species level by biochemical identification systems, Fourier-transform infrared-spectroscopy, Matrix-assisted laser desorption/ionization-time of flight mass spectrometry and partial rpoB sequencing, respectively. All ten isolates turned out to represent the same sequence type, strongly indicating a cluster of infections by clonally-related isolates as could be demonstrated for the first time for this species using multilocus sequence typing. Unequivocal demonstration of high relatedness of the isolates could also be demonstrated by Fourier-transform infrared-spectroscopy. All isolates were lacking the diphtheria toxin encoding tox-gene, but were phospholipase D-positive.

Conclusions

Our results indicate that water rats represent a suitable new host species that is prone to infection and must be regarded as a reservoir for potentially zoonotic Corynebacterium ulcerans. Furthermore, the applied methods demonstrated persistent infection as well as a very close relationship between all ten isolates.

Toxigenic Corynebacterium ulcerans in a fatal human case and her feline contacts, France, March 2014

In March 2014, a person in their eighties who was diagnosed with extensive cellulitis due to toxigenic Corynebacterium ulcerans died from multiple organ failure. Environmental investigation also isolated C. ulcerans in biological samples from two stray cats in contact with the case. This finding provides further evidence that pets can carry toxigenic C. ulcerans and may be a source of the infection in humans.

Access to diphtheria antitoxin for therapy and diagnostics

The most effective treatment for diphtheria is swift administration of diphtheria antitoxin (DAT) with conjunct antibiotic therapy. DAT is an equine immunoglobulin preparation and listed among the World Health Organization Essential Medicines. Essential Medicines should be available in functioning health systems at all times in adequate amounts, in appropriate dosage forms, with assured quality, and at prices individuals and the community can afford. However, DAT is in scarce supply and frequently unavailable to patients because of discontinued production in several countries, low economic viability, and high regulatory requirements for the safe manufacture of blood-derived products. DAT is also a cornerstone of diphtheria diagnostics but several diagnostic reference laboratories across the European Union (EU) and elsewhere routinely face problems in sourcing DAT for toxigenicity testing. Overall, global access to DAT for both therapeutic and diagnostic applications seems inadequate. Therefore--besides efforts to improve the current supply of DAT--accelerated research and development of alternatives including monoclonal antibodies for therapy and molecular-based methods for diagnostics are required. Given the rarity of the disease, it would be useful to organise a small stockpile centrally for all EU countries and to maintain an inventory of DAT availability within and between countries.

Toxigenic Corynebacterium ulcerans in human and non-toxigenic Corynebacterium diphtheriae in cat

Corynebacterium diphtheriae and Corynebacterium ulcerans are rarely isolated from clinical samples in Belgium. A case of toxigenic C. ulcerans in a woman is described, which confirms that this pathogen is still present. During investigation of the patient's cats, only a non-toxigenic toxin-bearing C. diphtheriae strain was detected.

Isolation and characterization of toxigenic Corynebacterium ulcerans from 2 closed colonies of cynomolgus macaques (Macaca fascicularis) in Japan

The aim of the present study was to determine the prevalence of infection by toxigenic Corynebacterium ulcerans in cynomolgus macaques (Macaca fascicularis) housed in an animal facility in Japan. Samples from the pharynges of animals from 2 closed colonies (colony A, n = 47; colony B, n = 21) were cultured. C. ulcerans grew from 43% and 47% of the samples from colonies A and B, respectively. The toxigenicity of these isolates was assessed by using PCR analysis for the diphtheria toxin gene and the Elek test and Vero cytotoxicity assay to detect diphtheria toxin. The proportion of macaques harboring toxigenic C. ulcerans was 6% in colony A and 29% in colony B. Analysis of diphtheria antitoxin neutralization titers in the sera revealed that 23% and 33% of macaques from colonies A and B, respectively, had a history of infection with toxigenic C. ulcerans. Pulsed-field gel electrophoresis of the toxigenic isolates showed that all of those recovered from macaques in colony B showed an identical genotype, suggesting that transmission of the organism occurred within the colony. However, isolates from colony A macaques showed 3 different genotypes, one of which was identical to the isolate from colony B. Additional studies evaluating the prevalence and transmission of toxigenic C. ulcerans within colonies of nonhuman primates are necessary to help control the spread of the infection. The current study is the first description of the isolation and characterization of toxigenic C. ulcerans from nonhuman primates in Japan.

Multiplex polymerase chain reaction to identify and determine the toxigenicity of Corynebacterium spp with zoonotic potential and an overview of human and animal infections

Corynebacterium diphtheriae, Corynebacterium ulcerans and Corynebacterium pseudotuberculosis constitute a group of potentially toxigenic microorganisms that are related to different infectious processes in animal and human hosts. Currently, there is a lack of information on the prevalence of disease caused by these pathogens, which is partially due to a reduction in the frequency of routine laboratory testing. In this study, a multiplex polymerase chain reaction (mPCR) assay that can simultaneously identify and determine the toxigenicity of these corynebacterial species with zoonotic potential was developed. This assay uses five primer pairs targeting the following genes: rpoB (Corynebacterium spp), 16S rRNA (C. ulcerans and C. pseudotuberculosis), pld (C. pseudotuberculosis), dtxR (C. diphtheriae) and tox [diphtheria toxin (DT) ]. In addition to describing this assay, we review the literature regarding the diseases caused by these pathogens. Of the 213 coryneform strains tested, the mPCR results for all toxigenic and non-toxigenic strains of C . diphtheriae, C. ulcerans and C. pseudotuberculosis were in 100% agreement with the results of standard biochemical tests and PCR-DT. As an alternative to conventional methods, due to its advantages of specificity and speed, the mPCR assay used in this study may successfully be applied for the diagnosis of human and/or animal diseases caused by potentially toxigenic corynebacterial species.

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.

Characterization and comparison of invasive Corynebacterium diphtheriae isolates from France and Poland

Corynebacterium diphtheriae, the agent of diphtheria, is rarely responsible for bacteremia. However, high numbers of bacteremia have been reported in countries with extensive immunization coverage. Here, we used molecular and phenotypic tools to characterize and compare 42 invasive isolates collected in France (including New Caledonia) and Poland over a 23-year period.

Corynebacterium epidermidicanis sp. nov., isolated from skin of a dog

A Gram-stain-positive, pleomorphic, oxidase-negative, non-motile isolate from the skin of a dog, designated strain 410(T), was subjected to comprehensive taxonomic characterization. Comparison of the 16S rRNA gene sequences revealed that the novel isolate showed highest similarities to the type strains of Corynebacterium humireducens, Corynebacterium diphtheriae, Corynebacterium pseudotuberculosis and Corynebacterium ulcerans (96.1-96.8 %). The quinone system consisted predominantly of MK-8(H(2)) and MK-9(H(2)). The polar lipid profile of strain 410(T) contained the major compounds diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, two unidentified phospholipids and four unidentified glycolipids. The polyamine pattern was composed of the major amines spermidine and spermine. In the fatty acid profile, predominantly straight-chain, saturated and mono-unsaturated fatty acids were detected (C(18 : 1)ω9c, C(16 : 1)ω7c, C(16 : 0)). These chemotaxonomic traits are in agreement with those reported for representatives of the genus Corynebacterium. Strain 410(T) tested negative for diphtheria toxin. Physiological properties as well as unique traits in the polar lipid profile could be used to distinguish strain 410(T) from the most closely related species. These data suggest that strain 410(T) represents a novel species of the genus Corynebacterium, for which we propose the name Corynebacterium epidermidicanis sp. nov. The type strain is 410(T) (= DSM 45586(T) = LMG 26322(T) = CCUG 60915(T)).

Proteomics of corynebacteria: From biotechnology workhorses to pathogens

Corynebacteria belong to the high G+C Gram-positive bacteria (Actinobacteria) and are closely related to Mycobacterium and Nocardia species. The best investigated member of this group of almost seventy species is Corynebacterium glutamicum, a soil bacterium isolated in 1957, which is used for the industrial production of more than two million tons of amino acids per year. This review focuses on the technical advances made in proteomics approaches during the last years and summarizes applications of these techniques with respect to C. glutamicum metabolic pathways and stress response. Additionally, selected proteome applications for other biotechnologically important or pathogenic corynebacteria are described.

Rapid detection and molecular differentiation of toxigenic Corynebacterium diphtheriae and Corynebacterium ulcerans strains by LightCycler PCR

The systemic symptoms of diphtheria are caused by the tox-encoded diphtheria toxin (DT) which is produced by toxigenic Corynebacterium spp. Besides the classical agent C. diphtheriae, the zoonotic pathogen C. ulcerans has increasingly been reported as an emerging pathogen for diphtheria. The reliable detection of toxigenic Corynebacterium spp. is of substantial importance for both diphtheria surveillance in the public health sector and the clinical workup of a patient with diphtherialike symptoms. Since the respective tox genes of C. diphtheriae and C. ulcerans differ from each other in both DNA and amino acid sequence, both tox genes should be covered by novel real-time PCR methods. We describe the development and validation of a LightCycler PCR assay which reliably recognizes tox genes from both C. diphtheriae and C. ulcerans and differentiates the respective target genes by fluorescence resonance energy transfer (FRET) hybridization probe melting curve analysis.

Corynebacterium ulcerans from diseased wild boars

Two Corynebacterium strains were isolated from lymph nodes of wild boars showing severe alterations caused by caseous lymphadenitis. The wild boars came from different districts in southern Germany; one was found dead, the other had been shot. The two Corynebacterium strains obtained were both positive for phospholipase D. Further analysis of biochemical profiles did not allow unambiguous differentiation between Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. Fourier-transformed infrared spectroscopy as well as partial sequencing of the genes for 16S rRNA and RNA polymerase beta subunit (rpoB) clearly identified both strains as Corynebacterium ulcerans. The tox gene for diphtheria toxin (DT) could be detected in both porcine isolates by PCR. Partial DNA sequencing of this tox gene showed significant differences from sequences described for other Corynebacterium ulcerans strains and a higher degree of similarity to that of Corynebacterium diphtheria. Production of diphtheria toxin could not be detected. These results indicate that wild game could be a reservoir for zoonotic Corynebacterium ulcerans.

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.

Diphtheria: a zoonotic disease in France?

Thanks to vaccination, diphtheria has almost disappeared in France. The case definition, used for mandatory notification, was expanded in 2003 to include toxin-producing strains of Corynebacterium ulcerans. We describe the epidemiology of diphtheria in France from 1990 to 2008. No cases occurred between 1990 and 2001. Since 2002, 19 cases have been reported: 4 cases due to Corynebacterium diphtheriae related to exposure in endemic countries, and 15 cases due to other corynebacteria, including 4 cases of pseudomembranous pharyngitis, mainly related to contact with domestic animals. High vaccination coverage in the population and sensitive surveillance need to be maintained. Moreover, control measures need to be adapted to the non-C. diphtheriae toxigenic species.

Corynebacterium ulcerans in an immunocompromised patient with diphtheria and her dog

Corynebacterium ulcerans causes zoonotic infections, such as diphtheria and extrapharyngeal infections. We report here the first case of a diphtheria-like illness caused by C. ulcerans in France and transmitted likely by a dog to an immunocompromised woman.

Detection of differences in the nucleotide and amino acid sequences of diphtheria toxin from Corynebacterium diphtheriae and Corynebacterium ulcerans causing extrapharyngeal infections

While Corynebacterium ulcerans can mimic classical diphtheria, extrapharyngeal infections are extremely rare. Sequencing of the diphtheria toxin (DT)-encoding tox gene of two C. ulcerans isolates from extrapharyngeal infections revealed differences from C. diphtheriae DT sequences, mainly in the translocation and receptor-binding domains. C. ulcerans supernatants were much less potent than supernatant from C. diphtheriae. A C. ulcerans DT-specific PCR is described below.

Rapid enzyme immunoassay for determination of toxigenicity among clinical isolates of corynebacteria

A rapid enzyme immunoassay (EIA) was developed for the phenotypic detection of diphtheria toxin among clinical isolates of corynebacteria. The assay uses equine polyclonal antitoxin as the capture antibody and an alkaline phosphatase-labeled monoclonal antibody, specific for fragment A of the toxin molecule, as the detecting antibody. The assay is rapid, sensitive, and specific: a final result is available within 3 h of colony selection, and the limits of detection are 0.1 ng of pure diphtheria toxin/ml. Toxigenicity could be detected with isolates grown on a diverse range of culture media, including selective agars. Toxin detection using the EIA was compared to that with the Elek test and PCR detection of fragment A of the diphtheria toxin (tox) gene, using 245 isolates of corynebacteria. The results for the EIA were in complete concordance with those of the Elek test: 87 toxigenic and 158 nontoxigenic isolates. Ten of the phenotypically nontoxigenic strains were found to contain fragment A of the tox gene but did not express the toxin protein. These isolates were found to be nontoxigenic in the Vero cell tissue culture cytotoxicity assay and were therefore nontoxigenic for diagnostic purposes. The EIA is a simple rapid phenotypic test which provides a definitive result on toxigenicity within one working day.

Current approaches to the laboratory diagnosis of diphtheria

Despite the success of mass immunization in many countries, diphtheria continues to play a major role as a potentially lethal resurgent infectious disease. Early, accurate diagnosis is imperative since delay in specific therapy may result in death. The microbiologic diagnosis of the disease, the identification of contacts and carriers, and the appropriate clinical management of these patients are therefore crucial. The epidemiology of diseases caused by Corynebacterium diphtheriae has changed dramatically over the decades, a situation that is highlighted by the resurgence of infections in the European region. These factors have strengthened the need for laboratories to screen for C. diphtheriae. Many modified and new methodologies are now used widely within laboratories for diphtheria diagnosis. Recent developments have focused upon methods for detection of the lethal and potent exotoxin produced by the causative organism, C. diphtheriae; this detection is the definitive test for the microbiologic diagnosis of diphtheria.

[Diphtheria and infections caused by Corynebacterium diphtheriae in 1997]

INTRODUCTION

Diphtheria is a reemerging disease. Two epidemics recently occurred in Algeria and Independent States Community, not so far from Europe. Imported cases were diagnosed in contiguous European countries. This review focuses on the data obtained from these epidemics, with particular emphasis on new clinical forms of Corynebacterium diphtheriae infections. CURRENTS KNOWLEDGE AND KEY POINTS: Sore throat with membranes is no longer the only clinical feature of diphtheria. However, patients' management is identical, with combination of antibiotics, injection of specific antisera, and immunization of patients' close contacts and relatives. French and American sero-epidemiological studies showed that antibody levels does not provide protection, particularly in the elderly. Adult populations would therefore be at risk every 10 years. Recent advances in molecular biology led to the development of gene amplification with polymerase chain reaction, that may be used for the detection of the toxin gene. They also promoted epidemiological surveys of circulating strains via ribotyping. Although this technic evidenced predominant strains in the various countries, genotypes encountered during an epidemics may differ. Besides diphtheria which has apparently been eradicated in France, systemic infections with non-toxigenic strains of C diphtheriae, such as endocarditis, septicemia and arthritis, are evenly diagnosed.

FUTURE PROSPECTS AND PROJECTS

A French national reference center for C diphtheriae has been recently created. This center collects most of the strains isolated in France, clinical data and assesses the toxigenicity of bacteria, allowing strict epidemiological survey.

Reversed passive latex agglutination assay for detection of toxigenic Corynebacterium diphtheriae

A reversed passive latex agglutination (RPLA) assay for determining the toxigenicity of Corynebacterium diphtheriae is presented. Rabbit antitoxin antiserum was raised by using commercially available diphtheria toxoid. This antiserum reacted with the diphtheria toxin when the culture supernatant was assayed by Western blotting, and it did not cross-react with other extracellular antigens. Affinity-purified antibodies for latex sensitization were obtained by using a Hi Trap N-hydroxysuccinimide-activated column. Demonstration of toxin in five of seven clinical isolates was in accordance with the PCR assay and the Vero cell cytotoxicity test. Culture of the bacteria for 6 h was sufficient for toxin production, and an additional 6 h was needed to observe latex agglutination. Therefore, diphtheria toxin can be detected in 12 h by this method. The lowest concentration of diphtheria toxin detectable by the RPLA assay was about 5 ng/ml. The RPLA assay can provide a convenient and reliable method for laboratories involved in the identification of toxinogenic corynebacteria.

Corynebacterium imitans sp. nov. isolated from patients with suspected diphtheria

A 5-month-old boy of a Romanian family traveling via Ukraine to Poland developed a respiratory disease that resembled and that was initially diagnosed as pharyngeal diphtheria. The child recovered after treatment with antidiphtheria antitoxin. A coryneform bacterium had been isolated from a nasopharyngeal specimen from the child and was initially identified as an atypical Corynebacterium diphtheriae strain. Seven adults who had contact with either the child or an adult contact person also developed symptoms of pharyngeal diphtheria, were also treated with antitoxin, and recovered uneventfully. Coryneform bacteria similar to that originating from the index patient were also isolated from the throat swabs of three adults. Detailed biochemical and chemotaxonomic investigations revealed that the coryneform bacteria belonged to the genus Corynebacterium and could be differentiated from all other defined species of this genus. Ribotyping and pulsed-field gel electrophoresis demonstrated that all four patients' isolates were of clonal origin. The diphtheria toxin gene and its product were not detected either by PCR assays or by the Elek test, making a possible disease association of the Corynebacterium more unlikely. Comparative 16S rRNA gene sequence analysis revealed that the coryneform bacterium represented a new subline within the genus Corynebacterium, for which the name Corynebacterium imitans sp. nov. is proposed. The type strain is NCTC 13015 (DSM 44264; CCUG 36877).

Comparison of traditional and molecular methods for typing nontoxigenic strains of Corynebacterium diphtheriae

Thirty-eight nontoxigenic strains of Corynebacterium diphtheriae isolated between 1987 and 1992 from clinical specimens of French patients were typed by biotyping, antibiograms, bacteriophage typing, ribotyping, and restriction analysis by pulsed-field gel electrophoresis (PFGE). Excellent correlation occurred between the genotypes defined by PFGE SfiI profiles or by ribotype BstEII profiles. Genotyping revealed seven genotype patterns among the 26 biotype mitis isolates, five among the nine biotype gravis isolates, and three among the three biotype belfanti isolates. Phage typing was nonreactive for nine of the 38 isolates. A combination of all the typing methods led to the identification of 19 different types of Corynebacterium diphtheriae.

Development of a direct PCR assay for detection of the diphtheria toxin gene

PCR has proved to be a reliable tool for the detection of the diphtheria toxin gene, tox, and its use has allowed for the rapid differentiation between toxigenic and nontoxigenic strains. In this study, this PCR was further developed, evaluated, and standardized to detect this gene directly from clinical specimens. Optimal conditions for collection, transport, and storage of the clinical specimens and isolation and purification of DNA from the clinical specimens were defined. With two sets of primers that detect the A and B subunits of the diphtheria toxin gene, sensitivity levels of 50 and 500 CFU/PCR mixture, respectively, were achieved. This PCR was evaluated with 162 clinical samples collected from patients with diphtheria and other upper respiratory tract infections, as well as from healthy individuals.

Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae

Non-toxigenic strains of Corynebacterium diphtheriae continue to cause disease within immunized populations. A subset of these corynebacteria carry the diphtheria toxin gene but in a cryptic form. To determine whether such strains might contribute to the re-emergence of functional toxin genes, the phages and tox mutations within three clone types were examined. tox-containing, beta-related phages were isolated from two of the strain types. The third isolate appeared to harbour a defective prophage. One of the tox- phages encoded truncated, yet enzymatically-active, forms of diphtheria toxin, suggesting that it had sustained a point mutation within the latter half of its toxin gene. In contrast, the other mutant phage did not elicit the production of either a cross-reacting material or an ADP-ribosylating activity. Complementation tests employing a series of double lysogens confirmed that the mutations responsible for the non-toxigenic phenotype of all of the phages were cis dominant. Given these findings, it is reasonable to hypothesize that tox+ genes can arise within human populations by either homologous recombination between two distinct tox- phages or spontaneous reversion within a single mutant allele.

Clinical and molecular study of Corynebacterium diphtheriae systemic infections in France. Coryne Study Group

Diphtheria is a disease with a long history that almost completely disappeared from developed countries. In addition, until 1987, systemic infections involving Corynebacterium diphtheriae were rare. However, in 1990, an epidemic occurred in Russia. These two circumstances have provided the stimulus to gain insight into the situation in France. In fact, between 1987 and 1993, a total of 59 C. diphtheriae strains were isolated. Epidemiological data were collected for patients from whom 40 strains were isolated from normally sterile sites, including 34 from blood cultures, and half of the bacteremic patients developed endocarditis. Osteoarticular involvement was noted in 11 of these 40 patients, including 5 bacteremic patients. The fatality rate following bacteremia was 36%, despite specific antibiotic treatment (beta-lactams and aminoglycosides). The mean age of the participants was 38 years, with half of the patients subsisting under low socioeconomic conditions and suffering from homelessness or alcoholism. Apparently, the skin turned out to be the major route of transmission in this reemerging disease. Eighty-eight percent of the isolates belonged to the C. diphtheriae biotype mitis. These were found predominantly in the Paris area, and most were of the same ribotype. Those isolates originating from the overseas territories (Guyana and New Caledonia) belonged to C. diphtheriae biotype gravis. No strains were positive for the tox gene by PCR. This study attests to the persistent circulation in France of C. diphtheriae in the form of systemic infections. The matter is especially significant since these strains are nontoxigenic and are of a unique ribotype. The strains are, however, sensitive to most antibiotics, although 20% are rifampin resistant.

A modified Elek test for detection of toxigenic corynebacteria in the diagnostic laboratory

The detection of toxigenicity among Corynebacterium diphtheriae and Corynebacterium ulcerans strains is the most important test for the microbiological diagnosis of diphtheria. Difficulties with current methods, in particular the Elek test, are well documented. We therefore describe a modified Elek test which provides an accurate result after only 16 h of incubation, in contrast to 48 h for the conventional test.

Clinical microbiology of coryneform bacteria

Coryneform bacteria are aerobically growing, asporogenous, non-partially-acid-fast, gram-positive rods of irregular morphology. Within the last few years, there has been a massive increase in the number of publications related to all aspects of their clinical microbiology. Clinical microbiologists are often confronted with making identifications within this heterogeneous group as well as with considerations of the clinical significance of such isolates. This review provides comprehensive information on the identification of coryneform bacteria and outlines recent changes in taxonomy. The following genera are covered: Corynebacterium, Turicella, Arthrobacter, Brevibacterium, Dermabacter. Propionibacterium, Rothia, Exiguobacterium, Oerskovia, Cellulomonas, Sanguibacter, Microbacterium, Aureobacterium, "Corynebacterium aquaticum," Arcanobacterium, and Actinomyces. Case reports claiming disease associations of coryneform bacteria are critically reviewed. Minimal microbiological requirements for publications on disease associations of coryneform bacteria are proposed.

Apport des méthodes de typage dans l'étude des souches de Corynebacterium diphtheriae

Corynebacterium diphtheriae is the causative agent of Diphtheria. This bacteria circulates throughout the world. Recently, two outbreaks occurred in New independent states (Russia, Ukraine...) and Algeria. Routine technics permit to study the strains of Corynebacterium diphtheriae : biotype, antibiotype, toxin gene detection. However, molecular biological tests (ribotyping, and pulsed field gel electrophoresis) are necessary to characterize these strains in the space and the time. The studies with international laboratories exchanges are recents and have permitted first results concerning the molecular epidemiology of C. diphtheriae strains.

Application of PCR for detection of toxigenic Corynebacterium diphtheriae strains isolated during the Russian diphtheria epidemic, 1990 through 1994

A total of 250 Corynebacterium diphtheriae isolates from clinical cases and carriers in Russia were assayed by PCR directed at the A subunit of the diphtheria toxin gene to distinguish toxigenic from nontoxigenic strains; 170 strains were positive as indicated by the presence of the 248-bp amplicon. The results of this PCR assay were in complete concordance with those of the standard immunoprecipitation assay (Elek), and the PCR assay is a useful tool for rapid identification in clinical laboratories.