Development and validation of a multiplex real-time PCR for detection of Clostridium chauvoei and Clostridium septicum

Development of real-time PCR assay for quantitative detection of Clostridium septicum

Cellulitis is an important disease in commercial turkey farms associated with significant economic loss. Although the etiology of cellulitis is not fully elucidated, Clostridium septicum (C. septicum) is one of the main causes of this infectious disease. In this study, we report the development of a quantitative real-time PCR (qRT PCR) assay targeting the alpha-toxin gene (csa), which involves a prior 15-cyle PCR using a nested pair of primers to increase the detection sensitivity. Additionally, the TaqMan probe was employed to increase the target-specificity of the assay. The performance of our nested qRT-PCR assay was evaluated using Clostridium isolates from turkey farms, representing both septicum and non-septicum species, as well as sponge swab samples from turkey farms. Our step-by-step development of the assay showed that the csa gene is a suitable target for specific detection of C. septicum strains and that the inclusion of nested PCR step significantly increased the detection sensitivity of the final qRT PCR assay. The performance of the assay was also validated by a high correlation of the threshold cycle numbers of the qRT PCR assay with the relative abundance of C. septicum read counts in 16S rRNA gene microbiota profiles of the C. septicum-containing samples from turkey farms.

60-year-old male with rapidly progressive pneumocephalus caused by Clostridium septicum in the setting of an occult colonic adenocarcinoma

Background

Disseminated Clostridium septicum infection is an uncommon complication associated with malignancies, particular colonic adenocarcinoma. The organism appears to preferentially colonize large masses in rare individuals and subsequently seed the blood via mucosal ulceration. This has rarely been reported to lead to central nervous system infection and, in several cases, rapidly progressive pneumocephalus. In the few cases reported, this was a universally fatal condition. The current case adds to the reports of this extremely rare complication and provides a unique and complete clinicopathologic characterization with autopsy examination, microscopy, and molecular testing.

Case Presentation

A 60-year-old man with no known past medical history was discovered having seizure-like activity and stroke-like symptoms. Blood cultures turned positive after six hours. Imaging revealed a large, irregular cecal mass as well as 1.4 cm collection of air in the left parietal lobe that progressed to over 7 cm within 8 h. By the following morning, the patient had lost all neurologic reflexes and died. Post-mortem examination revealed brain tissue with multiple grossly evident cystic spaces and intraparenchymal hemorrhage, while microscopic exam showed diffuse hypoxic-ischemic injury and gram-positive rods. Clostridium septicum was identified on blood cultures and was confirmed in paraffin embedded tissue from the brain by 16 S ribosomal sequencing and from the colon by C. septicum specific PCR.

Conclusions

C. septicum is an anaerobic, gram-positive rod that can become invasive and is strongly associated with gastrointestinal pathology including colonic adenocarcinomas. Central nervous system infection with rapidly progressive pneumocephalus is a rarely reported and universally fatal complication of disseminated C. septicum infection.

A review of cardiac blackleg in cattle, and report of 2 cases without skeletal muscle involvement in Argentina

Blackleg is an infectious disease caused by Clostridium chauvoei. Cardiac blackleg has been reported in ruminants as an uncommon presentation of the disease; its pathogenesis is not understood completely. We include here a literature review of cardiac blackleg and a description of 2 cases in 12-15-mo-old feedlot steers in Argentina. Fourteen of 1,190 steers died suddenly over a period of 10 d. Postmortem examinations were performed on 5 of these animals. Grossly, severe, diffuse, fibrinous pericarditis and pleuritis, multifocal necrohemorrhagic myocarditis, diffuse pulmonary congestion, mild splenomegaly, and moderate congestion of meningeal vessels were observed. No significant gross lesions were observed in the skeletal muscles of any animal. Histology was performed on 2 of the steers. The main microscopic features were necrotizing myocarditis with myriad intralesional gram-positive rods with subterminal spores plus fibrinosuppurative pericarditis and pleuritis. C. chauvoei was detected by immunohistochemistry and PCR in the myocardium of both animals. These findings confirm a diagnosis of cardiac blackleg in these 2 steers and presumptively in the other affected animals.

Production of neutralizing antibodies against the secreted Clostridium chauvoei toxin A (CctA) upon blackleg vaccination

Clostridium chauvoei is the etiologic agent of blackleg in cattle, inducing fever, severe myonecrosis, oedemic lesions and ultimately death of infected animals. The pathogen often results in such rapid death that antibiotic therapy is futile and thus vaccination is the only efficient strategy in order to control the disease. The β-barrel pore forming leucocidin Clostridium chauvoei toxin A (CctA) is one of the best characterised toxins of C. chauvoei and has been shown to be an important virulence factor. It has been reported to induce protective immunity and is conserved across C. chauvoei strains collected from diverse geographical locations for more than 50 years. The aim of this study was to identify the location of the CctA toxin during liquid culture fermentation and to use CctA to develop an in vitro assay to replace the current guinea pig challenge assay for vaccine potency in standard batch release procedures. We report that CctA is fully secreted in C. chauvoei culture and show that it is found abundantly in the supernatant of liquid cultures. Sera from cattle vaccinated with a commercial blackleg vaccine revealed strong haemolysin-neutralizing activity against recombinant CctA which reached titres of 1000 times 28 days post-vaccination. Similarly, guinea pig sera from an official potency control test reached titres of 600 times 14 days post-vaccination. In contrast, ELISA was not able to specifically measure anti-CctA antibodies in cattle serum due to strong cross-reactions with antibodies against other proteins present pre-vaccination. We conclude that haemolysin-neutralizing antibodies are a valuable measurement for protective immunity against blackleg and have the potential to be a suitable replacement of the guinea pig challenge potency test, which would forego the unnecessary challenge of laboratory animals.

Blackleg in cattle: Current understanding and future research perspectives- A review

Blackleg is an endogenous acute infection that principally affects cattle. The disease is caused by Clostridium chauvoei (C. chauvoei), an anaerobic spore forming bacterium. Control of this disease is based on stringent husbandry measures and scheduled vaccination plan. In recent years, the major virulence factors of C. chauvoei have been discovered and described. However, the pathogenesis of blackleg in cattle and in particular, circulation of the pathogen from point of entry to target tissues is yet not fully elucidated. This review summarizes the latest review of literature that significantly contributed for understanding the disease in cattle, and provides a foundation to preventive strategies.

First report of two complete Clostridium chauvoei genome sequences and detailed in silico genome analysis

Clostridium (C.) chauvoei is a Gram-positive, spore forming, anaerobic bacterium. It causes black leg in ruminants, a typically fatal histotoxic myonecrosis. High quality circular genome sequences were generated for the C. chauvoei type strain DSM 7528^T (ATCC 10092^T) and a field strain 12S0467 isolated in Germany. The origin of replication (oriC) was comparable to that of Bacillus subtilis in structure with two regions containing DnaA boxes. Similar prophages were identified in the genomes of both C. chauvoei strains which also harbored hemolysin and bacterial spore formation genes. A CRISPR type I-B system with limited variations in the repeat number was identified. Sporulation and germination process related genes were homologous to that of the Clostridia cluster I group but novel variations for regulatory genes were identified indicative for strain specific control of regulatory events. Phylogenomics showed a higher relatedness to C. septicum than to other so far sequenced genomes of species belonging to the genus Clostridium. Comparative genome analysis of three C. chauvoei circular genome sequences revealed the presence of few inversions and translocations in locally collinear blocks (LCBs). The species genome also shows a large number of genes involved in proteolysis, genes for glycosyl hydrolases and metal iron transportation genes which are presumably involved in virulence and survival in the host. Three conserved flagellar genes (fliC) were identified in each of the circular genomes. In conclusion this is the first comparative analysis of circular genomes for the species C. chauvoei, enabling insights into genome composition and virulence factor variation.

Clostridium chauvoei, an Evolutionary Dead-End Pathogen

Full genome sequences of 20 strains of Clostridium chauvoei, the etiological agent of blackleg of cattle and sheep, isolated from four different continents over a period of 64 years (1951–2015) were determined and analyzed. The study reveals that the genome of the species C. chauvoei is highly homogeneous compared to the closely related species C. perfringens, a widespread pathogen that affects human and many animal species. Analysis of the CRISPR locus is sufficient to differentiate most C. chauvoei strains and is the most heterogenous region in the genome, containing in total 187 different spacer elements that are distributed as 30 – 77 copies in the various strains. Some genetic differences are found in the 3 allelic variants of fliC1, fliC2 and fliC3 genes that encode structural flagellin proteins, and certain strains do only contain one or two alleles. However, the major virulence genes including the highly toxic C.chauvoei toxin A, the sialidase and the two hyaluronidases are fully conserved as are the metabolic and structural genes of C. chauvoei. These data indicate that C. chauvoei is a strict ruminant-associated pathogen that has reached a dead end in its evolution.

Patho-genetics of Clostridium chauvoei

The genomic sequence of Clostridium chauvoei, the etiological agent of blackleg, a severe disease of ruminants with high mortality specified by a myonecrosis reveals a chromosome of 2.8 million base-pairs and a cryptic plasmid of 5.5 kilo base-pairs. The chromosome contains the main pathways like glycolysis/gluconeogenesis, sugar metabolism, purine and pyrimidine metabolisms, but the notable absence of genes of the citric acid cycle and deficient or partially deficient amino acid metabolism for Histidine, Tyrosine, Phenylalanine, and Tryptophan. These essential amino acids might be acquired from host tissue damage caused by various toxins and by protein metabolism that includes 57 genes for peptidases, and several ABC transporters for amino acids import.

Dry-reagent-based PCR as a novel tool for the rapid detection of Clostridium spp

Improved conventional PCR techniques are required for the rapid on-site detection of human and animal diseases. In this context, a PCR method using dry-stored reagents intended for the detection of Clostridium spp. is presented. Basic PCR reagents (BSA, PCR buffer, MgCl2 and primers), which were dried on polyolefin matrices, showed stability at ambient temperatures for up to 10 months without any loss of functionality. An outstanding advantage of our amelioration is the elimination of PCR process errors caused by the improper storage and handling of liquid reagents. Moreover, our PCR-based amplification can be performed in less than 30 min, saving time compared with conventional detection methods. Thus, dry-reagent-based PCR is implementable in a suitcase-like modular device for the rapid on-site detection of microbial pathogens such as blackleg of ruminants caused by Clostridium chauvoei.

Development of a real time PCR Taqman assay based on the TPI gene for simultaneous identification of Clostridium chauvoei and Clostridium septicum

In the present study, a Taqman allelic discrimination assay based on three SNPs of the TPI gene is described. It was used as a differential diagnostic tool to detect blackleg and malignant edema. Sudden deaths of grazing ruminants, such as cattle, sheep and goats, which show clinical signs related to hyperacute infective processes, encouraged the development of a rapid and precise diagnostic molecular method. Specific primers and probes for Clostridium septicum and Clostridium chauvoei were designed on the basis of the TPI gene sequence. The multiplex PCR was tested on the DNA of a total of 57 strains, including 24 Clostridium chauvoei, 20 Clostridium septicum, 1 Bacillus anthracis and 12 other Clostridium spp. The DNA samples from Clostridium chauvoei and Clostridium septicum strains were amplified. Amplification of other DNA samples was not observed, with the exception of Clostridium tertium, which showed a weak positive signal. To avoid misdiagnosis, a confirmatory assay based on a Sybr green real time PCR was proposed. The authors confirmed the efficacy and the specificity of the test used in this study, which proved to be a useful tool for the diagnosis of clostridiosis that are often diagnosed using only traditional tools.