Pore-forming activity of alpha-toxin is essential for clostridium septicum-mediated myonecrosis

Exotoxins secreted by Clostridium septicum induce macrophage death: Implications for bacterial immune evasion mechanisms at infection sites

The induction of macrophage death is considered a potential mechanism by which components secreted by Clostridium septicum are used to evade the innate immune response and cause tissue damage. This study aimed to determine the effects of partially purified fractions of extracellular proteins secreted by C. septicum on the death of mouse peritoneal macrophages. Elicited mouse peritoneal macrophages were incubated with partially purified fractions of proteins secreted by C. septicum into the culture medium. After incubation, the protein fraction with a molecular weight ≥100 kDa caused significant cell death in macrophages, altered cell morphology, increased the expression of markers of apoptosis and autophagy, and increased the expression (protein and mRNA) of IL-10 and TNFα. Our data suggest that the proteins secreted by C. septicum (MW, ≥100 kDa) induce cell death in macrophages by promoting autophagy-triggered apoptosis. This study may contribute to our understanding of the molecular mechanism of immune evasion by C. septicum at the infection site.

Enhancing the Cytotoxicity and Apoptotic Efficacy of Parasporin-2-Derived Variants (Mpp46Aa1) on Cancer Cell Lines

Parasporin PS2Aa1, recently renamed Mpp46Aa1, is an anti-cancer protein known for its selectivity against various human cancer cell lines. We genetically modified native PS2Aa1 to create a library of approximately 100 mutants. From this library, we selected promising mutants based on their half-maximal inhibitory concentration (IC50) and sequence variations. In this study, Variant 3-35, with the G257V substitution, demonstrated increased cytotoxicity and selectivity against the colon cancer cell line SW480. Conversely, Variant N65, featuring substitutions N92D, K175R, and S218G, yielded the most favorable results against the cancer cell lines SW-620, MOLT-4, and Jurkat. The caspase 3/7 and 9, Annexin V-Cy3 and 6-GFDA activities, and, most notably, mitochondrial membrane permeabilization assays confirmed the apoptotic marker elevation. These findings indicate that residues 92, 175, 218, and 257 may play a critical role in the cytotoxic activity and selectivity. We successfully obtained genetically improved variants with substitutions at these key amino acid positions. Additionally, we conducted molecular dynamic simulations to explore the potential interactions between PS2Aa1 and the CD59 GPI-anchored protein. The simulation results revealed that residues 57, 92, and 101 were consistently present, suggesting their possible significance in the interactions between parasporin and the CD59 protein.

Clostridium septicum manifests a bile salt germinant response mediated by Clostridioides difficile csp gene orthologs

Clostridium septicum infections are highly predictive of certain malignancies in human patients. To initiate infections, C. septicum spores must first germinate and regain vegetative growth. Yet, what triggers the germination of C. septicum spores is still unknown. Here, we observe that C. septicum germinates in response to specific bile salts. Putative bile salt recognition genes are identified in C. septicum based on their similarity in sequence and organization to bile salt-responsive csp genes in Clostridioides difficile. Inactivating two of these csp orthologs (cspC-82 and cspC-1718) results in mutant spores that no longer germinate in the presence of their respective cognate bile salts. Additionally, inactivating the putative cspBA or sleC genes in C. septicum abrogates the germination response to all bile salt germinants, suggesting that both act at a convergent point downstream of cspC-82 and cspC-1718. Molecular dynamics simulations show that both CspC-82 and CspC-1718 bear a strong structural congruence with C. difficile's CspC. The existence of functional bile salt germination sensors in C. septicum may be relevant to the association between infection and malignancy.

Immunization of turkeys with Clostridium septicum alpha toxin-based recombinant subunit proteins can confer protection against experimental Clostridial dermatitis

Clostridial dermatitis (CD), caused by Clostridium septicum, is an emerging disease of increasing economic importance in turkeys. Currently, there are no effective vaccines for CD control. Here, two non-toxic domains of C. septicum alpha toxin, namely ntATX-D1 and ntATX-D2, were identified, cloned, and expressed in Escherichia coli as recombinant subunit proteins to investigate their use as potential vaccine candidates. Experimental groups consisted of a Negative control (NCx) that did not receive C. septicum challenge, while the adjuvant-only Positive control (PCx), ntATX-D1 immunization (D1) and ntATX-D2 immunization (D2) groups received C. septicum challenge. Turkeys were immunized subcutaneously with 100 μg of protein at 7, 8 and 9 weeks of age along with an oil-in-water nano-emulsion adjuvant, followed by C. septicum challenge at 11 weeks of age. Results showed that while 46.2% of birds in the PCx group died post-challenge, the rate of mortality in D1- or D2-immunization groups was 13.3%. The gross and histopathological lesions in the skin, muscle and spleen showed that the disease severity was highest in PCx group, while the D2-immunized birds had significantly lower lesion scores when compared to PCx. Gene expression analysis revealed that PCx birds had significantly higher expression of pro-inflammatory cytokine genes in the skin, muscle and spleen than the NCx group, while the D2 group had significantly lower expression of these genes compared to PCx. Peripheral blood cellular analysis showed increased frequencies of activated CD4+ and/or CD8+ cells in the D1 and D2-immunized groups. Additionally, the immunized turkeys developed antigen-specific serum IgY antibodies. Collectively, these findings indicate that ntATX proteins, specifically the ntATX-D2 can be a promising vaccine candidate for protecting turkeys against CD and that the protection mechanisms may include downregulation of C. septicum-induced inflammation and increased CD4+ and CD8+ cellular activation.

Characterization of immune responses and immunopathology in turkeys experimentally infected with clostridial dermatitis-producing strains of Clostridium septicum

Clostridium septicum is one of the major causative agents of clostridial dermatitis (CD), an emerging disease of turkeys, characterized by sudden deaths and necrotic dermatitis. Despite its economic burden on the poultry industry, the immunopathological changes and pathogen-specific immune responses are poorly characterized. Here, we used three strains of C. septicum, namely Str. A1, Str. B1 and Str. C1, isolated from CD field outbreaks, to experimentally infect turkeys to evaluate local (skin and muscle) and systemic (spleen) pathological and immunological responses. Results showed that while all three strains produced an acute disease, Str. A1 and B1 caused significantly higher mortality when compared to Str. C1. Gross and histopathology evaluation showed that birds infected with Str. A1 and B1 had severe inflammatory, edematous, granulomatous and necrotic lesions in the skin, muscle and spleen, while these lesions produced by Str. C1 were relatively less severe and mostly confined to skin and/or muscle. Immune gene expression in these tissues showed that Str. B1-infected birds had significantly higher expression of interleukin (IL)-1β, IL-6 and interferon (IFN)γ genes compared to uninfected control, suggesting a robust inflammatory response both locally as well as systemically. The transcription of IL-1β and IFNγ in the muscle or spleen of Str. A1-infected birds and IL-1β in the skin of Str. C1-infected group was also significantly higher than control. Additionally, Str. A1 or B1-infected groups also had significantly higher IL-4 transcription in these tissues, while birds infected with all three strains developed C. septicum-specific serum antibodies. Furthermore, splenic cellular immunophenotyping in the infected turkeys showed a marked reduction in CD4+ cells. Collectively, it can be inferred that host responses against C. septicum involve an acute inflammatory response along with antibody production and that the disease severity seem to depend on the strain of C. septicum involved in CD in turkeys.

A non-toxic recombinant Clostridium septicum α toxin induces protective immunity in mice and rabbits

Clostridium septicum alpha toxin (CSA) plays significant roles in ruminant's braxy. Genetically engineered CSA has been shown to function as a potential vaccine candidate in the prevention of the disease caused by Clostridium septicum. In the present study, we synthesized a non-toxic recombinant, rCSAm4/TMD by introducing four amino acid substitutions (C86L/N296A/H301A/W342A) and 11-amino-acid deletion (residues 212 to 222). Compared to recombinant CSA, rCSAm4/TMD showed no cytotoxicity to MDCK cells and was not fatal to mice. Moreover, rCSAm4/TMD could protect immunized mice against 5 × mouse LD100 (100% lethal dose) of crude CSA without obvious pathological change. Most importantly, rabbits immunized with rCSAm4/TMD produced high titers of neutralizing antibodies which protected the rabbits against crude CSA challenge. These data suggest that genetically detoxified rCSAm4/TMD is a potential subunit vaccine candidate against braxy.

Toxin-linked mobile genetic elements in major enteric bacterial pathogens

One of the fascinating outcomes of human microbiome studies adopting multi-omics technology is its ability to decipher millions of microbial encoded functions in the most complex and crowded microbial ecosystem, including the human gastrointestinal (GI) tract without cultivating the microbes. It is well established that several functions that modulate the human metabolism, nutrient assimilation, immunity, infections, disease severity and therapeutic efficacy of drugs are mostly of microbial origins. In addition, these microbial functions are dynamic and can disseminate between microbial taxa residing in the same ecosystem or other microbial ecosystems through horizontal gene transfer. For clinicians and researchers alike, understanding the toxins, virulence factors and drug resistance traits encoded by the microbes associated with the human body is of utmost importance. Nevertheless, when such traits are genetically linked with mobile genetic elements (MGEs) that make them transmissible, it creates an additional burden to public health. This review mainly focuses on the functions of gut commensals and the dynamics and crosstalk between commensal and pathogenic bacteria in the gut. Also, the review summarises the plethora of MGEs linked with virulence genes present in the genomes of various enteric bacterial pathogens, which are transmissible among other pathogens and commensals.

Immune Response Evaluation in Commercial Turkeys Affected with Clostridial Dermatitis

Clostridial dermatitis (CD), caused by Clostridium septicum and Clostridium perfringens, is an economically important emerging disease of turkeys characterized by sudden deaths and necrotic dermatitis. Immune responses in CD-affected commercial turkeys are poorly understood. In the present study, C. septicum was isolated from CD-affected commercial turkeys during a recent outbreak, and the tissues (skin, muscle, and spleen) were collected and analyzed for immune gene expression, along with samples from clinically healthy birds. The results showed that CD-affected turkeys had significantly higher levels of IL-1β, IL-6, IFNγ, and iNOS transcripts in the skin, muscle, and spleen tissues compared to healthy birds. Affected turkeys also had a significantly elevated transcription of toll-like receptor (TLR21) gene in the skin and spleen tissues, suggesting a role for this receptor in the immune recognition. The expression of IL-4 and IL-13 genes in the spleen and muscle was also significantly higher in the affected birds. Additional birds from the same affected and healthy farms examined for serology revealed that the CD-affected turkeys had significantly higher levels of serum IgM and IgY antibodies. Furthermore, in vitro stimulation of MQ-NCSU macrophages with C. septicum led to a significant transcriptional upregulation of IL-1β and IFNγ genes, while the IL-10 gene expression was downregulated. The surface expression of MHC-II protein and cellular production of nitric oxide were also significantly increased in the C. septicum-stimulated macrophages, indicating cellular activation. Collectively, our findings suggest that the host responses in CD-affected turkeys involve a robust inflammatory response as well as a response mediated by IL4/IL-13 cytokines that may aid in antibody-mediated immunity.

A non-toxic recombinant bivalent chimeric protein rETXm3CSAm4/TMD as a potential vaccine candidate against enterotoxemia and braxy

Clostridium perfringens epsilon toxin (ETX) and Clostridium septicum alpha toxin (CSA) are lethal and necrotizing toxins, which play key roles in enterotoxemia and braxy of ruminants, respectively. In the present study, we synthesized a bivalent chimeric protein rETX_m3CSA_m4/TMD comprising ETX_m3 (Y30A/H106P/Y196A) and CSA_m4/TMD (C86L/N296A/H301A/W342A and a deletion of residues 212 to 222). Compared with recombinant ETX and recombinant CSA, rETX_m3CSA_m4/TMD showed no cytotoxicity in Madin-Darby Canine Kidney cells and was not fatal to mice. Moreover, rETX_m3CSA_m4/TMD could protect immunized mice against 10 × mouse LD₁₀₀ of crude ETX or 3 × mouse LD₁₀₀ of crude CSA without obvious histopathologic difference. Most importantly, both rabbits and sheep immunized with rETX_m3CSA_m4/TMD produced high titers of neutralizing antibody which protected the animals against the challenge with crude ETX or crude CSA. These data suggest that genetically detoxified rETX_m3CSA_m4/TMD is a potential subunit vaccine candidate against enterotoxemia and braxy.

Clostridium myonecrosis - a rare and underdiagnosed condition in the elderly: a case with severe skipping lesions and an overview of treatment guidelines

We present an unusual and severe case of spontaneous clostridial myonecrosis (SCM) in an elderly patient, with severe skipping lesions spread throughout the body. CT imaging, combined with postmortem available blood cultures, confirmed the diagnosis. We noted an underrepresentation of SCM in the cohort of elderly patients (≥ 85 years), upon a review of case reports in the literature over the last decade. Given the worldwide demographic change resulting in an increase in the number of visits to emergency departments for this age group, it is likely that SCM is underdiagnosed in these elderly patients. This case report aims to increase awareness among emergency physicians to recognize the disease as well as to provide a treatment guideline, in order to provide better care and outcome.

Clostridium septicum α-toxin activates the NLRP3 inflammasome by engaging GPI-anchored proteins

Clostridium species are a group of Gram-positive bacteria that cause diseases in humans, such as food poisoning, botulism, and tetanus. Here, we analyzed 10 different Clostridium species and identified that Clostridium septicum, a pathogen that causes sepsis and gas gangrene, activates the mammalian cytosolic inflammasome complex in mice and humans. Mechanistically, we demonstrate that α-toxin secreted by C. septicum binds to glycosylphosphatidylinositol (GPI)-anchored proteins on the host plasma membrane, oligomerizing and forming a membrane pore that is permissive to efflux of magnesium and potassium ions. Efflux of these cytosolic ions triggers the activation of the innate immune sensor NLRP3, inducing activation of caspase-1 and gasdermin D, secretion of the proinflammatory cytokines interleukin-1β and interleukin-18, pyroptosis, and plasma membrane rupture via ninjurin-1. Furthermore, α-toxin of C. septicum induces rapid inflammasome-mediated lethality in mice and pharmacological inhibition of the NLRP3 inflammasome using MCC950 prevents C. septicum-induced lethality. Overall, our results reveal that cytosolic innate sensing of α-toxin is central to the recognition of C. septicum infection and that therapeutic blockade of the inflammasome pathway may prevent sepsis and death caused by toxin-producing pathogens.

First Comparative Analysis of Clostridium septicum Genomes Provides Insights Into the Taxonomy, Species Genetic Diversity, and Virulence Related to Gas Gangrene

Clostridium septicum is a Gram-positive, toxin-producing, and spore-forming bacterium that is recognized, together with C. perfringens, as the most important etiologic agent of progressive gas gangrene. Clostridium septicum infections are almost always fatal in humans and animals. Despite its clinical and agricultural relevance, there is currently limited knowledge of the diversity and genome structure of C. septicum. This study presents the complete genome sequence of C. septicum DSM 7534T type strain as well as the first comparative analysis of five C. septicum genomes. The taxonomy of C. septicum, as revealed by 16S rRNA analysis as well as by genomic wide indices such as protein-based phylogeny, average nucleotide identity, and digital DNA–DNA hybridization indicates a stable clade. The composition and presence of prophages, CRISPR elements and accessory genetic material was variable in the investigated genomes. This is in contrast to the limited genetic variability described for the phylogenetically and phenotypically related species Clostridium chauvoei. The restriction-modification (RM) systems between two C. septicum genomes were heterogeneous for the RM types they encoded. C. septicum has an open pangenome with 2,311 genes representing the core genes and 1,429 accessory genes. The core genome SNP divergence between genome pairs varied up to 4,886 pairwise SNPs. A vast arsenal of potential virulence genes was detected in the genomes studied. Sequence analysis of these genes revealed that sialidase, hemolysin, and collagenase genes are conserved compared to the α-toxin and hyaluronidase genes. In addition, a conserved gene found in all C. septicum genomes was predicted to encode a leucocidin homolog (beta-channel forming cytolysin) similar (71.10% protein identity) to Clostridium chauvoei toxin A (CctA), which is a potent toxin. In conclusion, our results provide first, valuable insights into strain relatedness and genomic plasticity of C. septicum and contribute to our understanding of the virulence mechanisms of this important human and animal pathogen.

Clostridium septicum myonecrosis in a pediatric patient with a self-reported penicillin allergy

Infections with Clostridium septicum are especially rare in pediatric patients. C. septicum is the most common cause of spontaneous myonecrosis and is usually associated with comorbid malignancy. Treatment of choice for cases of C. septicum myonecrosis is prompt and thorough surgical debridement and antimicrobial therapy with high dose penicillin. The experience and management of C. septicum infections in patients who are unable to take penicillin are not well described, and the optimal duration of therapy is largely unknown. We describe a case of spontaneous myonecrosis in a 14-year-old receiving cytotoxic chemotherapy for Burkitt's lymphoma who had an anecdotal history of a penicillin allergy. Her infection was initially treated with ceftazidime and metronidazole in concert with debridement but was ultimately cured with 3 weeks of intravenous penicillin therapy following a graded penicillin challenge in hospital. We observed a delayed inflammatory tissue response to a C. septicum skin, soft tissue infection that temporally corresponded to neutrophil reconstitution in our patient with severe neutropenia. Our experience demonstrates that C. septicum myonecrosis can present indolently and progress rapidly and highlights the need for clinical vigilance and repeat "second-look" surgeries. Our case also emphasizes the importance of de-labelling penicillin allergies.

Characterization of Paeniclostridium sordellii Metalloproteinase-1 in vitro and in an experimental model of infection

OBJECTIVE

Paeniclostridium sordellii is a pathogen that causes rapidly fatal infections characterized by severe edema, extreme leukemoid reaction and lack of an innate immune response. We recently identified a metalloproteinase of P. sordellii-1 (Mcs1) that cleaves human vascular cell adhesion molecule 1, an adhesion molecule important to hematopoietic precursor retention and leukocyte diapedesis. In the current study, we further characterize Mcs1 activity and investigate its role in pathogenesis.

METHODS

Mcs1 peptide cleavage sequence and activity conditions were identified using a semi-quantitative fluorescence-based reporter assay. Additional host targets for Mcs1 protease activity were tested and confirmed by gel electrophoreses and western blots. Finally, Mcs1 knock out (ΔMcs1) and complemented (cMcs1) strains were developed for assessment in our animal model of myonecrosis.

RESULTS

Data show that Mcs1 prefers aliphatic amino acid residues, I or L, especially when adjacent to negatively charged or noncharged-polar residues. In vitro, Mcs1 cleaved or partially cleaved human cell adhesion molecules, E-selectin and intracellular adhesion molecule-1 (ICAM-1), and mediators of innate immune infection defense, complement protein-3 and antimicrobial peptide LL-37. In vivo, infection with the ΔMcs1 P. sordellii strain had little effect on animal survival, tissue destruction or circulating white blood cell counts compared to wild type and cMcs1 strains.

CONCLUSIONS

Similar to proteolytic virulence factors from other pathogens, Mcs1 is a promiscuous protease that cleaves multiple human-host factors. Despite minimal impact of Mcs1 on the murine model of P. sordellii infection, it is worth considering its role in humans and other animal models.

Fatal Clostridium septicum myonecrosis from gastric perforation: A case report

Clostridial myonecrosis is a medical and surgical emergency which requires early and aggressive intervention to reduce mortality. We report a rare case of Clostridium septicum myonecrosis that disseminated hematogenously from a gastric perforation. The patient was afebrile and hemodynamically stable upon admission. He rapidly developed spontaneous clostridial myonecrosis and succumbed to septic shock 36 hours after presentation. In our extensive literature review this is the only case with blood cultures confirming Clostridium septicum bacteremia with a surgically confirmed gastric perforation source in the setting of spontaneous clostridial myonecrosis.

Clostridium septicum: A review in the light of alpha-toxin and development of vaccines

Clostridium septicum (CS) is a pathogen that can cause the death of animals in livestock worldwide through its main virulence factor, alpha-toxin (ATX). The aspects involved in diseases caused by ATX, such as economic impact, prevalence, and rapid clinical course, require that animals should be systematically immunized. This review provides an overview of CS in livestock farming and discusses current immunization methods. Currently, commercial vaccines available against CS involve the cultivation and inactivation of microorganisms and toxins using a time-consuming, expensive, and high biological risk-carrying production platform, and some have been reported to be ineffective. An alternative to this process is the recombinant DNA technology, although recombinant ATX obtained thus far is no longer efficient in stimulating protective antibody titers despite improvements in the production methods. On the other hand, immunized animals have highly favorable levels of survival when subjected to challenge tests, suggesting that high titers of circulating serum antibodies may not be representative of protection after immunization and that the non-immune cellular defenses associated with the particularities of the mechanism of action of ATX may be involved in the immune response of the host. To contribute to the future of global livestock farming through the development of more efficient recombinant vaccines, we suggest novel perspectives and strategies, such as the location of immunodominant epitopes, expression of relevant functional domains, and construction of chimeras, in the rational design of recombinant ATX.

Vaccination against pathogenic clostridia in animals: a review

Clostridium is a Gram-positive, rod-shaped, anaerobic, and spore-forming bacterium, which is found in the surrounding environments throughout the world. Clostridium species cause botulism, tetanus, enterotoxaemia, gas gangrene, necrotic enteritis, pseudomembranous colitis, blackleg, and black disease. Clostridium infection causes severe economic losses in livestock and poultry industries. Vaccination seems to be an effective way to control Clostridial diseases. This review discusses the toxins and vaccine development of the most common pathogenic Clostridium species in animals, including Clostridium perfringens, Clostridium novyi, Clostridium chauvoei, and Clostridium septicum. In this comprehensive study, we will review different kinds of clostridial toxins and the vaccines that are experimentally or practically available and will give a short description on each vaccine focusing on its applications, advantages, and disadvantages.

Molecular Cloning of a New Bi-Functional Fusion Protein of Clostridium perfringens Type A Alpha and Clostridium septicum Alpha Toxin Genes in E. coli

Background: A synthetic construct bi-functional protein fusion includes two protein domains, or proteins bind by a fragment. The synthetic construct is designed to achieve better characterize and new functionality. Therefore, having proper cells is essential for cloning fusion genes. Clostridium perfringens type A produces the alpha-toxin and can cause gas gangrene and gastrointestinal diseases. C. septicum produces the alpha-toxin and can cause non-traumatic and traumatic gas gangrene. Objectives: The current study aimed to investigate molecular cloning of a new bi-functional fusion protein of C. perfringens alpha (cpa) and C. septicum alpha (csa) toxin genes in E. coli TOP10. In silico analysis was used for the chimeric fusion protein structural prediction. Methods: To produce chimeric fusion protein, the alpha-alpha (α-α) fusion gene was designed according to nucleotide sequences of cpa (KY584046.1) and csa (JN793989.2) genes. Tertiary structural prediction and validation of the fusion protein were determined by online software. In the new synthetic construction, α-α fusion protein genes are bind via the linker AEAAAKEAAAKA. The linker was introduced between the two domains by fusion PCR. The synthetic fusion gene was cloned into the pUC57cloning vector and then transferred into the host cell. Results: Analysis of the chimeric protein fusion is showed using the I-TASSER server as C-score equal to -2.68 as well as Rampage software in order to confirm the geometrical model as a natural like protein. Also, 1.0% agarose gel electrophoresis of fusion PCR product and sequencing analysis revealed a DNA fragment length of 2346 bp. Screening gel electrophoresis showed 996 bp length, which the designed linker was contained in it. Gel electrophoresis of extracted and purified recombinant plasmid (pUC57/αα) showed that a pUC57/αα of 5056 bp. The digested recombinant pUC57/αα showed one 2.3 kb (our fusion gene) band and one 2.7 kb (pUC57) band. Conclusions: This study presented a new approach for the fusion of cpa and csa genes based on the fusion PCR strategy. According to the latest information, this is the first time that α-α fusion gene is designed and cloned into a suitable cloning vector.

Central residues of the amphipathic β-hairpin loop control the properties of Clostridium perfringens epsilon-toxin channel

Clostridium perfringens epsilon toxin (ETX) is a heptameric pore-forming toxin of the aerolysin toxin family. ETX is the most potent toxin of this toxin family and the third most potent bacterial toxin with high cytotoxic and lethal activities in animals. In addition, ETX shows a demyelinating activity in nervous tissue leading to devastating multifocal central nervous system white matter disease in ruminant animals. Pore formation in target cell membrane is most likely the initial critical step in ETX biological activity. Eight single to quadruple ETX mutants were generated by replacement of polar residues (serine, threonine, glutamine) in middle positions of the β-strands forming the β-barrel and facing the channel lumen with charged glutamic residues. Channel activity and ion selectivity were monitored in artificial lipid monolayer membranes and cytotoxicity was investigated in MDCK cells by the viability MTT test and propidium iodide entry. All the mutants formed channels with similar conductance in artificial lipid membranes and increasing cation selectivity for increasing number of mutations. Here, we show that residues in the central position of each β-strand of the amphipathic β-hairpin loop that forms the transmembrane pore, control the size and ion selectivity of the channel. While the highest cationic ETX mutants were not cytotoxic, no strict correlation was observed between ion selectivity and cytotoxicity.

Necrotizing Soft Tissue Infections: A Focused Review of Pathophysiology, Diagnosis, Operative Management, Antimicrobial Therapy, and Pediatrics

Background: Necrotizing fasciitis is a major health problem throughout the world. The purpose of this review is to assist providers with the care of these patients through a better understanding of the pathophysiology and management options. Methods: This is a collaborative review of the literature between members of the Surgical Infection Society of North America and World Society of Emergency Surgery. Results: Necrotizing fasciitis continues to be difficult to manage with the mainstay being early diagnosis and surgical intervention. Recognition of at-risk populations assists with the initiation of treatment, thereby impacting outcomes. Conclusions: Although there are some additional treatment strategies available, surgical debridement and antimicrobial therapy are central to the successful eradication of the disease process.

Vaccine Production to Protect Animals Against Pathogenic Clostridia

Clostridium is a broad genus of anaerobic, spore-forming, rod-shaped, Gram-positive bacteria that can be found in different environments all around the world. The genus includes human and animal pathogens that produce potent exotoxins that cause rapid and potentially fatal diseases responsible for countless human casualties and billion-dollar annual loss to the agricultural sector. Diseases include botulism, tetanus, enterotoxemia, gas gangrene, necrotic enteritis, pseudomembranous colitis, blackleg, and black disease, which are caused by pathogenic Clostridium. Due to their ability to sporulate, they cannot be eradicated from the environment. As such, immunization with toxoid or bacterin-toxoid vaccines is the only protective method against infection. Toxins recovered from Clostridium cultures are inactivated to form toxoids, which are then formulated into multivalent vaccines. This review discusses the toxins, diseases, and toxoid production processes of the most common pathogenic Clostridium species, including Clostridiumbotulinum, Clostridiumtetani, Clostridiumperfringens, Clostridiumchauvoei, Clostridiumsepticum, Clostridiumnovyi and Clostridiumhemolyticum.

Histotoxic Clostridial Infections

The pathogenesis of clostridial myonecrosis or gas gangrene involves an interruption to the blood supply to the infected tissues, often via a traumatic wound, anaerobic growth of the infecting clostridial cells, the production of extracellular toxins, and toxin-mediated cell and tissue damage. This review focuses on host-pathogen interactions in Clostridium perfringens-mediated and Clostridium septicum-mediated myonecrosis. The major toxins involved are C. perfringens α-toxin, which has phospholipase C and sphingomyelinase activity, and C. septicum α-toxin, a β-pore-forming toxin that belongs to the aerolysin family. Although these toxins are cytotoxic, their effects on host cells are quite complex, with a range of intracellular cell signaling pathways induced by their action on host cell membranes.

Sudden death due to gas gangrene caused by Clostridium septicum in goats

Background

Even though gas gangrene caused by Clostridium septicum in goats is mentioned in the classical textbooks, we have not managed to find any case description in the literature.

Case presentation

Clinical signs resembling gas gangrene such as subcutaneous bloating, edema and crepitation were detected at various body parts of nine pregnant animals at the ages of 2–3 years on a hair goat farm (n = 170) located in Bingol province, Eastern Turkey. Five of these suspected animals with severe clinical symptoms died within 2 days. Various samples such as internal organs, edematous skin and edema fluid collected from dead and live animals were analyzed for the presence of clostridial agents by histopathological and microbiological methods. As a result of macroscopic and microscopic examination, lesions of gas gangrene were detected. The suspected isolates were identified and confirmed as C. septicum by bacteriological and molecular methods.

Conclusion

The present study was the first to report identification of C. septicum as primary agent in the gas gangrene of goats.

Ethanolamine utilization supports Clostridium perfringens growth in infected tissues

Clostridium perfringens possesses the ethanolamine (EA) utilization (eut) system encoded within the eut operon, which utilizes the EA as a carbon, nitrogen and energy source. To determine the role of the eut system in C. perfringens growth, an in-frame deletion of the eutABC genes was made in strain HN13 to generate the eutABC-deleted mutant strain HY1701. Comparison of HN13 and HY1701 growth in media supplemented with 1.0% glucose and/or 1.0% EA showed that glucose enhanced the growth of both strains, whereas EA enhanced HN13 growth, but not that of HY1701, indicating that the eut system is necessary for C. perfringens to utilize EA. The two-component regulatory system EutVW is needed to induce eut gene expression in response to EA whereas the global virulence regulator VirRS differentially controlled eut gene expression depending on glucose and EA availability. To assess the role of the eut system in vivo, an equal number of HN13 and HY1701 cells were injected into the right thigh muscles of mice. Mice infected with HY1701 showed fewer symptoms than those injected with HN13. The mortality rate of mice infected with HY1701 tended to be lower than for mice infected with HN13. In addition, in infected tissues from mice injected with a mixture of HN13 and HY1701, HN13 outnumbered HY1701. PCR screening demonstrated that C. perfringens isolated from gas gangrene and sporadic diarrhea cases carried both eut genes and the perfringolysin O gene (pfoA) as well as the phospholipase C gene (plc). However, pfoA was not detected in isolates from food poisoning patients and healthy volunteers. Culture supernatants prepared from HN13 grown in media containing 7.5% sheep red blood cells induced significantly higher eutB expression levels compared to those from plc- and/or pfoA-deletion mutants. Together, these results indicate that the eut system plays a nutritional role for C. perfringens during histolytic infection.

Spontaneous C. septicum gas gangrene: A literature review

As the infectious disease paradigm undergoes a subtle shift, unusual infections associated with malignancy and immunosuppression are being increasingly reported. Spontaneous or non-traumatic Clostridium septicum infection is one such unusual infection which has gained prominence. This article aims to understand the pathophysiology, clinical manifestations and current trends in diagnosing and treating this rare but deadly infection. To understand the multifactorial causation of this infection a review of published cases of spontaneous C. septicum gas gangrene was performed and a total of 94 such cases were identified. Several factors were analyzed for each case: age, infection location and underlying illness, presenting signs and symptoms, neutropenia, gross pathology of the colon, antibiotic use, surgical intervention, and survival. A known or occult malignancy was present in 71% patients and an overall mortality of 67% was observed.

Low prevalence of Clostridium septicum fecal carriage in an adult population

Clostridium septicum is an uncommon cause of severe infection. Real-time PCR against the C. septicum-specific alpha-toxin gene (csa) was used to estimate the prevalence of this microbe in human stool from 161 asymptomatic community-dwelling adults and 192 hospitalized patients with diarrhea. All samples were negative, suggesting a low prevalence.

Opioid analgesics stop the development of clostridial gas gangrene

Gas gangrene is a potentially fatal disease that is primarily caused by the ubiquitous, anaerobic bacteria Clostridium perfringens and Clostridium septicum. Treatment is limited to antibiotic therapy, debridement of the infected tissue, and, in severe cases, amputation. The need for new treatment approaches is compelling. Opioid-based analgesics such as buprenorphine and morphine also have immunomodulatory properties, usually leading to faster disease progression. However, here we show that mice pretreated with buprenorphine and morphine do not die from clostridial myonecrosis. Treatment with buprenorphine after the onset of infection also arrested disease development. Protection against myonecrotic disease was specific to C. perfringens-mediated myonecrosis; buprenorphine did not protect against disease caused by C. septicum infection even though infections due to both species are very similar. These data provide the first evidence of a protective role for opioids during infection and suggest that new therapeutic strategies may be possible for the treatment of C. perfringens-mediated myonecrosis.

Necrotizing endometritis and isolation of an alpha-toxin producing strain of Clostridium septicum in a wild sooty mangabey from Côte d'Ivoire

Few lethal pathogens in wild-living primates have been described, and little is known about infectious diseases of the reproductive tract and their possible impact on health and reproduction. This report describes the pathology and isolation of an alpha-toxin producing strain of Clostridium septicum in a case of necrotizing endometritis in a wild sooty mangabey found dead in a tropical rainforest of West Africa.

Myonecrosis by Clostridium septicum in a dog, diagnosed by a new multiplex-PCR

Clostridial myositis is an acute, generally fatal toxemia that is considered to be rare in pet animals. The present report describes an unusual canine clostridial myositis that was diagnosed by a new multiplex-PCR (mPCR) designed for simultaneous identification of Clostridium sordellii, Clostridium septicum, Clostridium perfringens type A, Clostridium chauvoei, and Clostridium novyi type A. A ten-month-old male Rottweiler dog, that had displayed lameness and swelling of the left limb for 12 h, was admitted to a veterinary hospital. The animal was weak, dyspneic and hyperthermic, and a clinical examination indicated the presence of gas and edema in the limb. Despite emergency treatment, the animal died in only a few minutes. Samples of muscular tissue from the necrotic area were aseptically collected and plated onto defibrinated sheep blood agar (5%) in anaerobic conditions. Colonies suggestive of Clostridium spp. were submitted to testing by multiplex-PCR. Impression smears of the tissues, visualized with Gram and also with panoptic stains, revealed long rod-shaped organisms, and specimens also tested positive using the fluorescent antibody technique (FAT). The FAT and mPCR tests enabled a diagnosis of C. septicum myonecrosis in the dog.

Recurrent horizontal transfer of bacterial toxin genes to eukaryotes

In this work, we report likely recurrent horizontal (lateral) gene transfer events of genes encoding pore-forming toxins of the aerolysin family between species belonging to different kingdoms of life. Clustering based on pairwise similarity and phylogenetic analysis revealed several distinct aerolysin sequence groups, each containing proteins from multiple kingdoms of life. These results strongly support at least six independent transfer events between distantly related phyla in the evolutionary history of one protein family and discount selective retention of ancestral genes as a plausible explanation for this patchy phylogenetic distribution. We discuss the possible roles of these proteins and show evidence for a convergent new function in two extant species. We hypothesize that certain gene families are more likely to be maintained following horizontal gene transfer from commensal or pathogenic organism to its host if they 1) can function alone; and 2) are immediately beneficial for the ecology of the organism, as in the case of pore-forming toxins which can be utilized in multicellular organisms for defense and predation.

Multifaceted interactions of bacterial toxins with the gastrointestinal mucosa

The digestive tract is one of the ecosystems that harbors the largest number and greatest variety of bacteria. Among them, certain bacteria have developed various strategies, including the synthesis of virulence factors such as toxins, to interact with the intestinal mucosa, and are responsible for various pathologies. A large variety of bacterial toxins of different sizes, structures and modes of action are able to interact with the gastrointestinal mucosa. Some toxins, termed enterotoxins, directly stimulate fluid secretion in enterocytes or cause their death, whereas other toxins pass through the intestinal barrier and disseminate by the general circulation to remote organs or tissues, where they are active. After recognition of a membrane receptor on target cells, toxins can act at the cell membrane by transducing a signal across the membrane in a hormone-like manner, by pore formation or by damaging membrane compounds. Other toxins can enter the cells and modify an intracellular target leading to a disregulation of certain physiological processes or disorganization of some structural architectures and cell death. Toxins are fascinating molecules, which mimic or interfere with eukaryotic physiological processes. Thereby, they have permitted the identification and characterization of new natural hormones or regulatory pathways. Besides use as protective antigens in vaccines, toxins offer multiple possibilities in pharmacology, such as immune modulation or specific delivery of a protein of interest into target cells.

The cysteine protease α-clostripain is not essential for the pathogenesis of Clostridium perfringens-mediated myonecrosis

Clostridium perfringens is the causative agent of clostridial myonecrosis or gas gangrene and produces many different extracellular toxins and enzymes, including the cysteine protease α-clostripain. Mutation of the α-clostripain structural gene, ccp, alters the turnover of secreted extracellular proteins in C. perfringens, but the role of α-clostripain in disease pathogenesis is not known. We insertionally inactivated the ccp gene C. perfringens strain 13 using TargeTron technology, constructing a strain that was no longer proteolytic on skim milk agar. Quantitative protease assays confirmed the absence of extracellular protease activity, which was restored by complementation with the wild-type ccp gene. The role of α-clostripain in virulence was assessed by analysing the isogenic wild-type, mutant and complemented strains in a mouse myonecrosis model. The results showed that although α-clostripain was the major extracellular protease, mutation of the ccp gene did not alter either the progression or the development of disease. These results do not rule out the possibility that this extracellular enzyme may still have a role in the early stages of the disease process.

An outbreak of gangrenous dermatitis in commercial broiler chickens

The present report describes an outbreak of gangrenous dermatitis (GD) infection in a commercial poultry farm in Delaware involving 34-day-old broiler chickens. In addition to obvious clinical signs, some GD-affected broilers also showed severe fibrino-necrotic enteritis and large numbers of Gram-positive rods in the necrotic tissue. Histopathological findings included haemorrhage, degeneration and necrosis of parenchymatous cells, especially of skin, muscle, and intestine. Immunofluorescence staining revealed Clostridium-like bacilli in the skin and the intestine. Both Clostridium perfringens and Clostridium septicum genomic sequences were identified by polymerase chain reaction in bacterial cultures isolated from the skin, muscle, and intestine, and in the frozen tissues from the GD-affected birds. Serological analysis demonstrated that both affected and clinically healthy birds from the same house had high serum antibody titres against C. perfringens, C. septicum, Eimeria, chick anaemia virus, and infectious bursal disease virus. These results are discussed in the context of the relationship between the different Clostridium spp. and the pathogenesis of GD.

Clostridial toxins

Clostridia produce the highest number of toxins of any type of bacteria and are involved in severe diseases in humans and other animals. Most of the clostridial toxins are pore-forming toxins responsible for gangrenes and gastrointestinal diseases. Among them, perfringolysin has been extensively studied and it is the paradigm of the cholesterol-dependent cytolysins, whereas Clostridium perfringens epsilon-toxin and Clostridium septicum alpha-toxin, which are related to aerolysin, are the prototypes of clostridial toxins that form small pores. Other toxins active on the cell surface possess an enzymatic activity, such as phospholipase C and collagenase, and are involved in the degradation of specific cell-membrane or extracellular-matrix components. Three groups of clostridial toxins have the ability to enter cells: large clostridial glucosylating toxins, binary toxins and neurotoxins. The binary and large clostridial glucosylating toxins alter the actin cytoskeleton by enzymatically modifying the actin monomers and the regulatory proteins from the Rho family, respectively. Clostridial neurotoxins proteolyse key components of neuroexocytosis. Botulinum neurotoxins inhibit neurotransmission at neuromuscular junctions, whereas tetanus toxin targets the inhibitory interneurons of the CNS. The high potency of clostridial toxins results from their specific targets, which have an essential cellular function, and from the type of modification that they induce. In addition, clostridial toxins are useful pharmacological and biological tools.

Malignant Edema in Postpartum Dairy Cattle

Five cases of postparturient vulvovaginitis and metritis in cattle caused by Clostridium septicum (malignant edema) are described in the current report. The diagnosis was established based on detection of C. septicum by culture and fluorescent antibody test. All animals were Holsteins, and 4 were primiparous (the parity of 1 animal was not reported). All animals developed clinical signs 1–3 days after calving, consisting of swelling of perineal and perivulvar areas, fever, and depression. Perineal, perivulvar, and perivaginal gelatinous and often hemorrhagic edema was consistently observed on gross examination. Longitudinal vulvar, vaginal, cervical, and uterine body tears, covered by fibrinous exudates, were also present. Microscopically, vulvar, vaginal, and uterine mucosae were multifocally necrotic and ulcerated. Large Gram-positive rods, some with subterminal spores, were present within the edematous subcutaneous and submucosal tissues. Clostridium septicum was demonstrated by culture and/or fluorescent antibody test in tissues of most animals. These cases of malignant edema were considered to be produced by C. septicum and predisposed by the trauma occurring during parturition.

Development and application of new mouse models to study the pathogenesis of Clostridium perfringens type C Enterotoxemias

Clostridium perfringens type C isolates cause enterotoxemias and enteritis in humans and livestock. While the major disease signs and lesions of type C disease are usually attributed to beta toxin (CPB), these bacteria typically produce several different lethal toxins. Since understanding of disease pathogenesis and development of improved vaccines is hindered by the lack of small animal models mimicking the lethality caused by type C isolates, in this study we developed two mouse models of C. perfringens type C-induced lethality. When inoculated into BALB/c mice by intragastric gavage, 7 of 14 type C isolates were lethal, whereas when inoculated intraduodenally, these strains were all lethal in these mice. Clinical signs in intragastrically and intraduodenally challenged mice were similar and included respiratory distress, abdominal distension, and neurological alterations. At necropsy, the small, and occasionally the large, intestine was dilated and gas filled in most mice developing a clinical response. Histological changes in the gut were relatively mild, consisting of attenuation of the mucosa with villus blunting. Inactivation of the CPB-encoding gene rendered the highly virulent type C strain CN3685 avirulent in the intragastric model and nearly nonlethal in the intraduodenal model. In contrast, inactivation of the genes encoding alpha toxin and perfringolysin O only slightly decreased the lethality of CN3685. Mice could be protected against lethality by intravenous passive immunization with a CPB antibody prior to intragastric challenge. This study proves that CPB is a major contributor to the systemic effects of type C infections and provides new mouse models for investigating the pathogenesis of type C-induced lethality.

Clostridium septicum alpha-toxin forms pores and induces rapid cell necrosis

Alpha-toxin is the unique lethal virulent factor produced by Clostridium septicum, which causes traumatic or non-traumatic gas gangrene and necrotizing enterocolitis in humans. Here, we analyzed channel formation of the recombinant septicum alpha-toxin and characterized its activity on living cells. Recombinant septicum alpha-toxin induces the formation of ion-permeable channels with a single-channel conductance of about 175pS in 0.1M KCl in lipid bilayer membranes, which is typical for a large diffusion pore. Septicum alpha-toxin channels remained mostly in the open configuration, displayed no lipid specificity, and exhibited slight anion selectivity. Septicum alpha-toxin caused a rapid decrease in the transepithelial electrical resistance of MDCK cell monolayers grown on filters, and induced a rapid cell necrosis in a variety of cell lines, characterized by cell permeabilization to propidium iodide without DNA fragmentation and activation of caspase-3. Septicum alpha-toxin also induced a rapid K(+) efflux and ATP depletion. Incubation of the cells in K(+)-enriched medium delayed cell death caused by septicum alpha-toxin or epsilon-toxin, another potent pore-forming toxin, suggesting that the rapid loss of intracellular K(+) represents an early signal of pore-forming toxins-mediated cell necrosis.

Programmed cellular necrosis mediated by the pore-forming alpha-toxin from Clostridium septicum

Programmed necrosis is a mechanism of cell death that has been described for neuronal excitotoxicity and ischemia/reperfusion injury, but has not been extensively studied in the context of exposure to bacterial exotoxins. The α-toxin of Clostridium septicum is a β-barrel pore-forming toxin and a potent cytotoxin; however, the mechanism by which it induces cell death has not been elucidated in detail. We report that α-toxin formed Ca²⁺-permeable pores in murine myoblast cells, leading to an increase in intracellular Ca²⁺ levels. This Ca²⁺ influx did not induce apoptosis, as has been described for other small pore-forming toxins, but a cascade of events consistent with programmed necrosis. Ca²⁺ influx was associated with calpain activation and release of cathepsins from lysosomes. We also observed deregulation of mitochondrial activity, leading to increased ROS levels, and dramatically reduced levels of ATP. Finally, the immunostimulatory histone binding protein HMGB1 was found to be released from the nuclei of α-toxin-treated cells. Collectively, these data show that α-toxin initiates a multifaceted necrotic cell death response that is consistent with its essential role in C. septicum-mediated myonecrosis and sepsis. We postulate that cellular intoxication with pore-forming toxins may be a major mechanism by which programmed necrosis is induced.

Clostridium septicum is a highly virulent pathogen that causes spontaneous gas gangrene or clostridial myonecrosis. The essential virulence factor of C. septicum is a β-barrel toxin, α-toxin, that forms small pores in host cell membranes. This toxin is frequently described as a hemolysin, because the formation of these pores causes lysis of red blood cell cells due to membrane disruption. However, this description does not recognize additional effects that may be observed in nucleated host cells, which are more sensitive to α-toxin. We investigated how nucleated cells responded to α-toxin by treating a physiologically relevant muscle cell line with purified toxin and monitoring the response using various assays. We observed α-toxin-mediated programmed cellular necrosis that culminated in the release of the immunostimulatory molecule, HMGB1. This mechanism of cell death induction is consistent with the extensive necrosis that is evident in C. septicum-mediated myonecrosis and with the overwhelming sepsis that frequently contributes to the high mortality rate. These results represent an important advance in the understanding of the toxicity of β-barrel pore-forming toxins and how they may contribute to necrotic and systemic disease pathology.