Exudative pharyngitis possibly due to Corynebacterium pseudodiphtheriticum, a new challenge in the differential diagnosis of diphtheria

Corynebacterium pseudodiphtheriticum has rarely been reported to cause disease in humans, despite its common presence in the flora of the upper respiratory tract. We report here a case of exudative pharyngitis with pseudomembrane possibly caused by C. pseudodiphtheriticum in a 4-year-old girl. The case initially triggered clinical and laboratory suspicion of diphtheria. Because C. pseudodiphtheriticum can be easily confused with Corynebacterium diphtheriae in Gram stain, clarification of its role in the pathogenesis of exudative pharyngitis in otherwise healthy persons is of public health importance. Simple and rapid screening tests to differentiate C. pseudodiphtheriticum from C. diphtheriae should be performed to prevent unnecessary concern in the community and unnecessary outbreak control measures.

Analysis of heterogeneity of Corynebacterium diphtheriae toxin gene, tox, and its regulatory element, dtxR, by direct sequencing

The largest diphtheria outbreak in the developed world since the 1960s is in progress in the Russian Federation. Seventy-two Corynebacterium diphtheriae strains from throughout Russia and the Ukraine, selected for temporal and geographic diversity, and 6 reference and control strains were assayed by DNA direct sequencing, and DNA sequences of their diphtheria toxin gene, tox, and the regulatory dtxR gene, were compared to those of the Park-Williams no. 8 strain (PW8). Twenty-eight C. diphtheriae strains had entire tox sequences identical to that of the PW8 strain. Among the remaining 40 strains which were toxigenic, 4 point mutations were detected in the tox gene, one within the A and three within the B subunit gene. All four were silent mutations, indicating that diphtheria toxin is highly conserved at the amino acid sequence level; therefore, changes in the efficacy of the current vaccines would be unlikely to occur. Within the open reading frame of the regulatory dtxR gene, 35 point mutations were detected. Only 15 strains had entire dtxR sequences identical to that of the PW8 strain. Nine amino acid substitutions were found in the carboxyl half of dtxR: 22 and 25 strains differed from the PW8 strain in one and two amino acids, respectively. Given that naturally occurring variations of dtxR might be associated with increased diphtheria toxin production, studies to investigate the association of these point mutations and amino acid substitutions with quantified toxin production in the strains causing the current epidemic are under way.

Construction of an epitope vector utilising the diphtheria toxin B-subunit

An immunogenic loop within the diphtheria toxin has been deleted from the B-subunit by a modification of the inverse polymerase chain reaction (IPCR) and replaced by a unique restriction endonuclease site. An oligonucleotide encoding an identified epitope sequence from the major outer membrane protein of Neisseria meningitidis of similar size and structure to that deleted has been introduced into the restriction site. Expression of the resulting chimeric B-subunit from Escherichia coli yielded a protein that was recognised by a panel of antibodies specific for the meningococcal epitope. Initial immunisation data suggest that this protein could elicit an antibody response against both diphtheria toxin and meningococcal proteins.

Molecular epidemiology of diphtheria in Russia, 1985-1994

The largest diphtheria outbreak in the developed world since the 1960s began in the Russian federation in 1990. One hundred fifty-six Corynebacterium diphtheriae strains from throughout Russia, selected for temporal and geographic diversity, were assayed by ribotyping and multilocus enzyme electrophoresis (MEE). These tests showed significant genetic diversity within the C. diphtheriae species, and ribotyping and MEE data generally correlated well with epidemiologic data. A distinct clonal group of C. diphtheriae isolates (ET 8 complex) emerged in Russia in 1990 as the current outbreak began, and as the outbreak has progressed, these organisms have made up increasingly larger proportions of the strains that are isolated. Furthermore, the main characteristic of the epidemic strains is a specific combination of ET 8 and ribotypes G1 and G4. This study confirms the epidemiologic utility of the molecular subtyping methods that detected the epidemic clone and addresses the clone's origin and relation to C. diphtheriae from throughout Russia.

[The genetic typing of Corynebacterium diphtheriae strains by the polymerase chain reaction with universal primers]

The use of polymerase chain reaction (UP-PCR with universal primers for the genetic typing of 85 C. diphtheriae strains, isolated from patients and carriers at the period of the epidemic, has shown that a single natural clone of biovar gravis seems to prevail in North Western Russia. UP-PCR is an effective too for the rapid intraspecific typing of strains on the molecular-genetic level and for the study of the circulation of C.diphtheriae epidemic clones.

Heterogeneity of diphtheria toxin gene, tox, and its regulatory element, dtxR, in Corynebacterium diphtheriae strains causing epidemic diphtheria in Russia and Ukraine

Diphtheria toxin (tox) and its regulatory element (dtxR) from 72 Corynebacterium diphtheriae strains isolated in Russia and Ukraine before and during the current diphtheria epidemic were studied by PCR-single-strand conformation polymorphism analysis (PCR-SSCP). Twelve sets of primers were constructed (eight for tox and four for dtxR), and three regions within tox and all four regions of dtxR showed significant variations in the number and/or sizes of the amplicons. Two to four different SSCP patterns were identified in each of the variable regions; subsequently, tox and dtxR could be classified into 6 and 12 different types, respectively. The great majority of epidemic strains from both Russia and Ukraine had tox types 3 and 4, and only in a single preepidemic strain isolated in Russia were all eight tox regions identical to those of C. diphtheriae Park-Williams No. 8 (tox type 1). Epidemic strains from Ukraine can easily be identified by dtxR type 5, while the majority of the Russian epidemic strains have dtxR of types 2 and 8. No differences in the tox regions between mitis and gravis biotype strains were observed. However, dtxR types 2, 5, and 8 were identified only in the gravis biotype, and dtxR type 1 was characteristic for the mitis biotype strains. PCR-SSCP is a simple and rapid method for the identification of variable tox and dtxR regions that allows for the clear association of tox and dtxR types with strains of distinct temporal and/or geographic origins.

Non-toxigenic Corynebacterium diphtheriae biovar gravis: evidence for an invasive clone in a south-eastern Australian community

OBJECTIVE

To determine the prevalence and clonality of non-toxigenic Corynebacterium diphtheriae biovar gravis in a community with two cases of endocarditis caused by this organism.

SETTING

A Koorie (Aboriginal) community in Gippsland, eastern Victoria, in 1994.

METHODS

Nose and throat swabs were collected from 359 community contacts of the cases and cultured for C. diphtheriae. Strains isolated from the contacts were compared by pulsed-field gel electrophoresis (after digestion with Sma1, Not1 and Sfi1) with those from the invasive cases in the same community, another invasive case in Victoria, a cluster of invasive cases in New South Wales (NSW) (1990-1991), and other stored strains isolated from skin ulcers and sore throats.

RESULTS

Non-toxigenic strains of C. diphtheriae biovar gravis were isolated from throat swabs of five of the case contacts. Uniform DNA patterns were found for the two community cases, the other Victorian case, nine of ten isolates from NSW, and the five throat isolates from case contacts.

CONCLUSION

An invasive clone of C. diphtheriae biovar gravis appears to have been responsible for the three Victorian cases of endocarditis. It was also present among case contacts and responsible for previous invasive cases in NSW. Prophylactic treatment should be considered for clearly defined contacts in all instances where C. diphtheriae is isolated from a normally sterile site, regardless of the toxigenic nature of the strain.

Cloning and sequence analysis of the Corynebacterium diphtheriae dtxR homologue from Streptomyces lividans and S. pilosus encoding a putative iron repressor protein

The iron-regulated promoter involved in desferrioxamine B synthesis of Streptomyces pilosus contains a region homologous to the iron repressor (DtxR)-binding site of the diphtheria toxin gene promoter in Corynebacterium diphtheriae [Günter et al., J. Bacteriol. 175 (1993) 3295-3302]. Here, we report the cloning and sequencing of the putative Streptomyces iron repressor gene, homologous to dtxR of C. diphtheriae. The N-terminal 139 amino acids of the deduced protein are 73% identical to DtxR.

Characterization of an iron-dependent regulatory protein (IdeR) of Mycobacterium tuberculosis as a functional homolog of the diphtheria toxin repressor (DtxR) from Corynebacterium diphtheriae

The DtxR protein from Corynebacterium diphtheriae is an iron-dependent repressor that regulates transcription from the tox, IRP1, and IRP2 promoters. A gene from virulent Mycobacterium tuberculosis H37Rv was recently shown to encode a protein, here designated iron-dependent regulator (IdeR), that is almost 60% homologous to DtxR from C. diphtheriae. A 750-bp PCR-derived DNA fragment carrying the M. tuberculosis ideR allele was subcloned to both high- and low-copy-number vectors. In Escherichia coli, transcription from the C. diphtheriae tox, IRP1, and IRP2 promoters was strongly repressed by ideR under high-iron conditions, and ideR restored normal iron-dependent expression of the corynebacterial siderophore in the C. diphtheriae dtxR mutant C7(beta)hm723. The M. tuberculosis IdeR protein was overexpressed in E. coli and purified to near homogeneity by nickel affinity chromatography. Gel mobility shift experiments revealed that IdeR bound to a DNA fragment that carried the C. diphtheriae tox promoter/operator sequence. DNAse I footprint analysis demonstrated that IdeR, in the presence of Cd2+, Co2+, Fe2+, Mn2+, Ni2+, or Zn2+, protected an approximately 30-bp region on DNA fragments carrying the tox, IRP1, or IRP2 promoter/operator sequences. IdeR reacted very weakly in Western blots (immunoblots) with antiserum against the C. diphtheriae DtxR protein, suggesting that the immunodominant epitopes of DtxR may be located in its poorly conserved carboxyl-terminal domain.

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.

Evaluation of the applicability of amplified rDNA-restriction analysis (ARDRA) to identification of species of the genus Corynebacterium

The 16S rRNA genes (rDNA) of 50 strains belonging to 26 different coryneform bacterial species and genomospecies and of the type strain of Rhodococcus equi were enzymatically amplified. Amplified rDNA restriction analysis (ARDRA) with the enzymes AluI, CfoI and RsaI was carried out. The combination of the ARDRA patterns obtained after restriction with these three different enzymes enabled the differentiation between the following species: Corynebacterium accolens (number of strains = 2), C. afermentans subsp. afermentans (2), C. afermentans subsp. lipophilum (2), C. amycolatum (3), CDC coryneform group ANF-1-like (1), CDC coryneform group ANF-3-like (1), C. cystitidis (1), C. diphtheriae (4), C. jeikeium (3), C. macginleyi (2), C. minutissimum (1), C. pilosum (1), C. pseudotuberculosis (2), C. renale (2), C. striatum (2), C. urealyticum (3), C. xerosis (1), CDC coryneform groups B-1 (2), B-3 (2), F-1, genomospecies 1 and 2 (6), G, genomospecies 1 (1) and G, genomospecies 2 (2). The following strains or species could not be differentiated from each other: C. pseudodiphtheriticum (2) from C. propinquum (former CDC coryneform group ANF-3) (2), CDC coryneform group F-1, genomospecies 1 (4) from genomospecies 2 (2) and C. jeikeium genomospecies A (1) from genomospecies C (2). ARDRA may represent a possible alternative for identification of coryneforms, since this technique enabled the identification of most coryneforms tested and since DNA extraction (i.e. cell lysis by boiling), amplification, restriction and electrophoresis can be carried out within 8 hours. This might allow quick identification of C. diphtheriae and other possible pathogens of the genus Corynebacterium.

Farnesylation of CaaX-tagged diphtheria toxin A-fragment as a measure of transfer to the cytosol

Diphtheria toxin binds to receptor-positive cells through its B-fragment, the toxin is then endocytosed, and the low pH in endosomes triggers the translocation of the enzymatically active A-fragment to the cytosol. A synchronous release of A-fragments into the cytosol can be induced by exposing cells with surface-bound toxin to low pH. We have used this protein translocation system to develop a novel method to study whether or not a protein is exposed to the cytosol. Protein farnesylation is a cytosolic modification signaled by a C-terminal CaaX motif, and to visualize the translocation process, we added a farnesylation signal to the toxin A-fragment. The A-fragment with an added CaaX motif was farnesylated within 1 h after exposure of cells with surface-bound toxin to low pH, and also A-fragment translocated from endosomes was quantitatively farnesylated. The results indicate that all cell-mediated reduction of the toxin implicates translocation of the A-fragment to the cytosol. The farnesylation was inhibited by lovastatin, the alkylating agent NEM, and the peptidomimetic farnesylation inhibitor B581. Farnesylated A-fragment partitioned preferentially into the detergent phase upon extraction with Triton X-114. Our data suggest that farnesylation of a CaaX tag is generally applicable as a cytosolic marker, and this strategy for monitoring protein transfer to the cytosol may have considerable potential for studying the transport to the cytosol of proteins added externally to cells.

The Corynebacterium xerosis composite transposon Tn5432 consists of two identical insertion sequences, designated IS1249, flanking the erythromycin resistance gene ermCX

Analysis of the 50-kb R-plasmid pTP10 from the clinical isolate Corynebacterium xerosis M82B revealed that the erythromycin resistance gene, ermCX, is located on a 4524-bp composite transposable element, Tn5432. The ends of Tn5432 are identical, direct repeats of an insertion sequence, designated IS1249, encoding a putative transposase of the IS256 family. IS1249 consists of 1385 bp with 45/42 imperfect terminal inverted repeats. The nucleotide sequence of the 1754-bp Tn5432 central region is 99% identical to the previously sequenced erythromycin resistance region of the Corynebacterium diphtheriae plasmid pNG2. It encodes the erythromycin resistance gene, ermCX, and an ORF homologous to the amino-terminal end of the transposase of IS31831 from Corynebacterium glutamicum. Transposons with regions flanking the insertion sites were recovered from the C. glutamicum chromosome by a plasmid rescue technique. Insertion of Tn5432 created 8-bp target site duplications. A Tn5432-induced isoleucine/valine-auxotrophic mutant was found to carry the transposon in the 5' region of the ilvBNC cluster; in pTP10 the transposon is inserted in a region similar to replication and partitioning functions of the Enterococcus faecalis plasmid pAD1 and the Agrobacterium tumefaciens plasmid pTAR.

Genetic relationships of Corynebacterium diphtheriae strains isolated from a diphtheria case and carriers by restriction fragment length polymorphism of rRNA genes

In the present study we report the results of an analysis, based on ribotyping of Corynebacterium diphtheriae intermedius strains isolated from a 9 years old child with clinical diphtheria and his 5 contacts. Quantitative analysis of RFLPs of rRNA was used to determine relatedness of these 7 C.diphtheriae strains providing support data in the diphtheria epidemiology. We have also tested those strains for toxigenicity in vitro by using the Elek's gel diffusion method and in vivo by using cell culture method on cultured monkey kidney cell (VERO cells). The hybridization results revealed that the 5 C.diphtheriae strains isolated from contacts and one isolated from the clinical case (nose case strain) had identical RFLP patterns with all 4 restriction endonucleases used, ribotype B. The genetic distance from this ribotype and ribotype A (throat case strain), that we initially assumed to be responsible for the illness of the patient, was of 0.450 showing poor genetic correlation among these two ribotypes. We found no significant differences concerned to the toxin production by using the cell culture method. In conclusion, the use of RFLPs of rRNA gene was successful in detecting minor differences in closely related toxigenic C.diphtheriae intermedius strains and providing information about genetic relationships among them.

Cloning of a Corynebacterium diphtheriae iron-repressible gene that shares sequence homology with the AhpC subunit of alkyl hydroperoxide reductase of Salmonella typhimurium

To understand how Corynebacterium diphtheriae responds to iron limitation, we compared the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) protein profiles of both wild-type cells and iron uptake mutants grown in either high- or low-iron medium. The removal of iron by ethylene diamine di-(o-hydroxy-phenyl acetic acid) from the growth medium of wild-type cells resulted in induction of at least 14 polypeptides. DirA, a major iron-repressible polypeptide, was purified from wild-type cells by preparative SDS-PAGE, and the dirA structural gene was isolated from a genomic library of nontoxigenic C. diphtheriae. The nucleotide sequence of dirA was determined, and the deduced amino acid sequence of DirA revealed strong homologies with the AhpC subunit of Salmonella typhimurium alkyl hydroperoxide reductase and polypeptides of other microorganisms associated with oxidation reduction activity. Like AhpC, cloned DirA reduced the susceptibility of an Escherichia coli ahp mutant to cumene hydroperoxide, suggesting that DirA has alkyl hydroperoxide reductase activity.

Molecular epidemiology of Corynebacterium diphtheriae from northwestern Russia and surrounding countries studied by using ribotyping and pulsed-field gel electrophoresis

A selection of 100 Corynebacterium diphtheriae isolates from asymptomatic carriers and clinical cases from five regions in northwestern Russia were examined. Six additional isolates from patients in Finland and Estonia with epidemiological links to Russia were also examined. All isolates were characterized by biotyping, toxigenicity testing, ribotyping, and pulsed-field gel electrophoresis (PFGE). Hybridization of genomic DNA digested with BstEII revealed five ribotype patterns among the biotype gravis isolates (G1 through G5) and two patterns among the biotype mitis isolates (M1 and M2). PFGE using SfiI was not able to distinguish between ribotypes G1, G2, and G4. The predominant ribotype pattern, G1, found in cases of disease in all the areas studied, appears to be disseminating, in view of the isolates received from imported cases in Finland and Estonia. Among the 106 isolates examined, 68 produced pattern G1 and 24 produced pattern M1. Most of the M1 isolates were from the Leningrad Oblast region. Distinct ribotypes such as G2, G3, G4, G5, and M2 could represent endemic disease.

Taxonomy of Corynebacterium diphtheriae and related taxa, with recognition of Corynebacterium ulcerans sp. nov. nom. rev

Levels of genomic DNA relatedness were determined using a S1 nuclease procedure for reference bacteria identified as biotypes of Corynebacterium diphtheriae, biovars of Corynebacterium pseudotuberculosis, and 'Corynebacterium ulcerans'. These results showed that the three species are separate taxa at the genomospecies level whereas biotypes and biovars are closely related genomically within each species. Phylogenetic analyses of small-subunit rDNA sequences revealed that 'Corynebacterium ulcerans' forms a tight cluster with Corynebacterium pseudotuberculosis within the robust branch that groups all Corynebacterium sequenced to date. Therefore, we propose that the species incertae sedis 'C. ulcerans' should be conclusively recognized as a distinct species within the genus Corynebacterium with strain CCUG 2708 = NCTC 7910 as type strain. This species is characterized by urease production and fermentation of glycogen.

Polymerase chain reaction for the detection of toxigenic Corynebacterium diphtheriae

Several conventional methods have been described for the detection of Corynebacterium diphtheriae toxin, including Elek immunodiffusion, tissue culture using VERO cells and guinea pig inoculation. All these methods have the disadvantage of being either slow to complete or technically demanding, particularly when performed infrequently. We examined 64 strains of C. diphtheriae by PCR and Elek immunodiffusion, and strains showing a positive result in either assay were inoculated into guinea pigs. Seven isolates were positive in both Elek and PCR assays and subsequently positive in guinea pig inoculation assay. One isolate was negative in Elek testing but positive in PCR assay and guinea pig inoculation. All other isolates were negative in both Elek and PCR assays. The PCR assay is rapid with cycling and detection complete within 3-4 hrs of receipt of strains. PCR has now become the routine method for detection of C. diphtheriae toxin in our laboratory.

Molecular cloning, DNA sequence analysis, and characterization of the Corynebacterium diphtheriae dtxR homolog from Brevibacterium lactofermentum

A homolog of the Corynebacterium diphtheriae dtxR gene was isolated from Brevibacterium lactofermentum. The product of the B. lactofermentum dtxR gene was immunoreactive with polyclonal anti-DtxR antibodies and functioned as an iron-activated repressor capable of regulating the expression of beta-galactosidase from a diphtheria tox promoter/operator transcriptional fusion in recombinant Escherichia coli. The extents of induction by increasing concentrations of the chelator 2,2'-dipyridyl were identical in cells expressing DtxR from either C. diphtheriae or B. lactofermentum.

[Use of a DNA-DNA hybridization method for studying Corynebacterium diphtheriae strains]

In addition to traditional tests, a battery of DNA probes was used to characterize 134 toxigenic and 125 nontoxigenic C.diphtheriae strains isolated in Russia in 1986-1989. 2.5% of nontoxigenic strains carried the determinants of both toxin subunits A and B, and 20% possessed at least a fragment of the gene determining toxin synthesis. Optimal conditions of hybridization technology were found. The method may be used as an alternative to traditional techniques in diagnostic studies and screenings.

Iron, DtxR, and the regulation of diphtheria toxin expression

In recent years considerable advances have been made in the understanding of the molecular basis of iron-mediated regulation of diphtheria toxin expression. The tox gene has been shown to be regulated by the heavy metal ion-activated regulatory element DtxR. In the presence of divalent heavy metal ions, DtxR becomes activated and binds to a 9 bp interrupted palindromic sequence. The consensus-binding site has been determined by both the sequence analysis of DtxR-responsive operators cloned from genomic libraries of Corynebacterium diphtheriae as well as by in vitro genetic methods using cyclic amplification of selected targets (CASTing). It is now clear that DtxR functions as a global iron-sensitive regulatory element in the control of gene expression in C. diphtheriae. In addition, the metal ion-activation domain of DtxR is being characterized by both mutational analysis and determination of the X-ray structure at 3.0 A resolution.