The exotoxins of Corynebacterium ulcerans

Rare human skin infection with Corynebacterium ulcerans: transmission by a domestic cat

Corynebacterium ulcerans is mainly known for its ability to cause animal infections. Some strains of C. ulcerans produce diphtheria toxin, which can cause life-threatening cardiopathies and neuropathies in humans. Human cutaneous C. ulcerans infection is a very rare disease that mimics classical cutaneous diphtheria. We present a very rare case of a C. ulcerans skin infection caused by a non-diphtheria toxin-producing strain of C. ulcerans that resolved after 3 weeks of therapy with amoxicillin-clavulanate. A pet cat was the probable source of infection. The presence of C. ulcerans in the mouth of the cat was confirmed by 16S rRNA gene analysis and the API Coryne system. In cases of human infection with potentially toxigenic corynebacteria, it is important to determine the species and examine the isolate for diphtheria toxin production. If toxigenicity is present, diphtheria antitoxin should be administered immediately. Carriers and potential infectious sources of C. ulcerans include not only domestic livestock but also pet animals. For the primary prevention of disease caused by diphtheria toxin-producing corynebacteria, vaccination with diphtheria toxoid is recommended.

Development of a rapid 1-h fluorescence-based cytotoxicity assay for Listeria species

Listeria monocytogenes is cytotoxic to the lymphocyte-origin hybridoma Ped-2E9 cell line. The relative cytotoxicity can be calculated by assaying the release of alkaline phosphatase (ALP) from the infected cell line. In this study, a fluorogenic substrate (4-methylumbelliferyl phosphate, MUP) was used to quantify the ALP activity. The assay is 3.5-fold more sensitive than the colorimetric-based assay and requires only 1 h to differentiate virulent from avirulent strains. In addition to various Listeria species, 27 different common foodborne or clinical microorganisms were tested with the fluorescence-based cytotoxicity assay and only six cultures (Bacillus cereus, Citrobacter freundii, Serratia marcescens, Pseudomonas putida, Corynebacterium glutamicum and Micrococcus luteus) showed cytotoxic effects similar to L. monocytogenes. To use this assay as a confirmatory test for virulent L. monocytogenes suspect strains, pure cultures must be isolated from the sample prior to testing.

Infection of the skin caused by Corynebacterium ulcerans and mimicking classical cutaneous diphtheria

Extrapharyngeal infections caused by Corynebacterium ulcerans have rarely been reported previously, and diphtheria toxin production has usually not been addressed. This case demonstrates that strains of C. ulcerans that produce diphtheria toxin can cause infections of the skin that completely mimic typical cutaneous diphtheria, thereby potentially providing a source of bacteria capable of causing life-threatening diseases in the patient's environment. Therefore, it is recommended to screen wound swabs for coryneform bacteria, identify all isolates, carefully assess possible toxin production, and send questionable strains to a specialist or a reference laboratory.

Characterization of detergent-soluble proteins of Corynebacterium pseudotuberculosis

Whole cells and culture supernatant of isolates of Corynebacterium pseudotuberculosis were studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting (immunoblotting). SDS-PAGE analysis of detergent-solubilized whole cells revealed more than 20 bands in silver-stained gels. However, the SDS-soluble proteins that are present in all the isolates of the bacterium can be separated into four groups, as follows, (i) high molecular mass proteins that are greater than 119 kDa, (ii) a set of three proteins with molecular mass of 84, 64 and 58 kDa, (iii) a doublet consisting of proteins of molecular mass 33 to 30 kDa, and (iv) low molecular mass proteins of 25 to 20 kDa. SDS-PAGE analysis of ammonium sulphate concentrated culture supernatant demonstrated more than seven bands in silver-stained gels ranging in molecular mass from 64-14 kDa. Sera from goats with C. pseudotuberculosis-induced disease were used to probe immunoblots of electrophoresed SDS-soluble proteins. Ten or more SDS-soluble proteins from whole cells, ranging in molecular mass from 119-20 kDa were recognized by antibodies in sera of naturally infected goats. These sera also recognized up to five molecules ranging from 64-30 kDa, on immunoblots of ammonium sulfate concentrated culture supernatant.

Arcanobacterium haemolyticum phospholipase D is genetically and functionally similar to Corynebacterium pseudotuberculosis phospholipase D

Arcanobacterium haemolyticum, a pathogen of the human upper respiratory tract and other systems, has been reported to produce soluble toxins, including a phospholipase D (PLD). We confirmed production of PLD by this organism and cloned and sequenced pld. Arcanobacterial PLD (PLD-A) was found to be a protein of approximately 31.5 kDa with a pI of approximately 9.4. Cosmid cloning, followed by subcloning into phagemid pBluescriptIISK+, yielded Escherichia coli(pAh140), a recombinant with a gene product corresponding to PLD-A. Evidence of PLD activity was found by three assays in supernatant fluid of cultures of E. coli(pAh140) and A. haemolyticum, but not in E. coli(pBluescriptIISK+). Experiments to determine if this protein was secreted were not conducted, but previous work with PLD from Corynebacterium pseudotuberculosis suggested that the presence of the enzyme in culture supernatant fluids was due to lysis of E. coli rather than to active transport. Antibodies in polyclonal sera from goats immunized with native or recombinant PLD-A neutralized native and recombinant PLD-A activity, and antibodies against native or recombinant PLD from C. pseudotuberculosis (PLD-P) partially neutralized native and recombinant PLD-A. Antibodies prepared against recombinant PLD-A labelled both recombinant and native PLD-A in Western blots (immunoblots) and dot blots, but antibodies against PLD-P did not. Sequencing of the insert in pAh140 revealed an open reading frame of 930 bp coding for 309 amino acids, including a putative signal sequence of 26 amino acids (3.2 kDa, determined on the basis of homology with the 24-amino-acid signal sequence of pld from C. pseudotuberculosis bv. ovis) and the mature PLD protein (31.5 kDa). Sequence comparisons of coding regions revealed 65% DNA homology with pld genes from C. pseudotuberculosis and Corynebacterium ulcerans. Comparison of amino acid sequences revealed 64% homology of PLD-A both with PLD-P and with PLD produced by C. ulcerans.

Nasopharyngeal Corynebacterium ulcerans: a different diphtheria

A case of toxigenic Corynebacterium ulcerans infection is presented. The diagnosis was delayed and no anti-toxin administered. A nasopharyngeal biopsy was complicated by severe haemorrhage necessitating a post nasal pack. A brief review of the pathology and treatment of Corynebacterium ulcerans is given.

Coryneform bacteria in infectious diseases: clinical and laboratory aspects

Coryneform isolates from clinical specimens frequently cannot be identified by either reference laboratories or research laboratories. Many of these organisms are skin flora that belong to a large number of taxonomic groups, only 40% of which are in the genus Corynebacterium. This review provides an update on clinical presentations, microbiological features, and pathogenic mechanisms of infections with nondiphtheria Corynebacterium species and other pleomorphic gram-positive rods. The early literature is also reviewed for a few coryneforms, especially those whose roles as pathogens are controversial. Recognition of newly emerging opportunistic coryneforms is dependent on sound identification schemes which cannot be developed until cell wall analyses and nucleic acid studies have defined the taxonomic groups and all of the reference strains within each taxon have been shown by molecular methods to be authentic members. Only then can reliable batteries of biochemical tests be selected for distinguishing each taxon.

Cloning and expression of the phospholipase D gene from Corynebacterium pseudotuberculosis in Escherichia coli

A toxic phospholipase D (PLD) is putatively involved in pathogenesis of Corynebacterium pseudotuberculosis infections. We report here the cloning and expression of the PLD gene (pld) in Escherichia coli. A cosmid library of DNA from C. pseudotuberculosis biovar ovis isolate Whetten 1 was constructed and screened for PLD-producing recombinants by plating them on LB agar containing sheep erythrocytes and equi factors. One recombinant, designated pCpO1, yielded a gene product which displayed synergistic hemolytic and sphingomyelinase D activities, both of which are characteristic of PLD. Subcloning into pUC19 yielded a recombinant, pCpO50, which contained a 1.8-kilobase insert. Analysis of supernatant fluids and cell extracts of cultures of E. coli(pCpO50) revealed sphingomyelinase activity and a protein of about 31,000 Mr, neither of which were detected in E. coli(pUC19). The 31-kilodalton protein also reacted with antibodies in serum from a sheep naturally infected with C. pseudotuberculosis, serum which also contained PLD-neutralizing antibodies. When Southern blots of BamHI digests of DNA from biovar ovis and biovar equi isolates of C. pseudotuberculosis were probed with pCpO50, bands of 4.8 and 1.9 kilobases, respectively, were seen, suggesting that the genome organization of pld is different for isolates from the two biovars.

Corynebacterium ulcerans in humans and cattle in North Devon

A case of Corynebacterium ulcerans sore throat in a community that drank raw milk from its own farm led to the discovery of another symptomless human infection. Eight cows in the herd were found to be infected and the intermittent pattern of excretion was demonstrated in another cow followed through its lactation. Further evidence of milk infected by C. ulcerans was found by examining all raw milk samples submitted to the laboratory. Two other human cases were diagnosed in Devon during the period of this investigation.

Production of diphtheria toxin by selected isolates of Corynebacterium ulcerans and Corynebacterium pseudotuberculosis

We determined the diphtheria toxin phenotype of specially selected isolates of Corynebacterium ulcerans and Corynebacterium pseudotuberculosis (C. ovis). All produced proteins similar in size and immunological structure to diphtheria toxin. As with diphtheria toxin, they exhibited ADP-ribosylating activity, and their synthesis was regulated by iron.