Molecular basis of toxicity of Clostridium perfringens epsilon toxin

The Molecular Architecture and Mode of Action of Clostridium perfringens ε-Toxin

Clostridium perfringens ε-toxin has long been associated with a severe enterotoxaemia of livestock animals, and more recently, was proposed to play a role in the etiology of multiple sclerosis in humans. The remarkable potency of the toxin has intrigued researchers for many decades, who suggested that this indicated an enzymatic mode of action. Recently, there have been major breakthroughs by finding that it is a pore-forming toxin which shows exquisite specificity for cells bearing the myelin and lymphocyte protein (MAL) receptor. This review details the molecular structures of the toxin, the evidence which identifies MAL as the receptor and the possible roles of other cell membrane components in toxin binding. The information on structure and mode of action has allowed the functions of individual amino acids to be investigated and has led to the creation of mutants with reduced toxicity that could serve as vaccines. In spite of this progress, there are still a number of key questions around the mode of action of the toxin which need to be further investigated.

Inhibition of pathogenic microbes in oral infectious diseases by natural products: Sources, mechanisms, and challenges

The maintenance of oral health is of utmost importance for an individual's holistic well-being and standard of living. Within the oral cavity, symbiotic microorganisms actively safeguard themselves against potential foreign diseases by upholding a multifaceted equilibrium. Nevertheless, the occurrence of an imbalance can give rise to a range of oral infectious ailments, such as dental caries, periodontitis, and oral candidiasis. Presently, clinical interventions encompass the physical elimination of pathogens and the administration of antibiotics to regulate bacterial and fungal infections. Given the limitations of various antimicrobial drugs frequently employed in dental practice, the rising incidence of oral inflammation, and the escalating bacterial resistance to antibiotics, it is imperative to explore alternative remedies that are dependable, efficacious, and affordable for the prevention and management of oral infectious ailments. There is an increasing interest in the creation of novel antimicrobial agents derived from natural sources, which possess attributes such as safety, cost-effectiveness, and minimal adverse effects. This review provides a comprehensive overview of the impact of natural products on the development and progression of oral infectious diseases. Specifically, these products exert their influences by mitigating dental biofilm formation, impeding the proliferation of oral pathogens, and hindering bacterial adhesion to tooth surfaces. The review also encompasses an examination of the various classes of natural products, their antimicrobial mechanisms, and their potential therapeutic applications and limitations in the context of oral infections. The insights garnered from this review can support the promising application of natural products as viable therapeutic options for managing oral infectious diseases.

Is Clostridium perfringens epsilon toxin associated with multiple sclerosis?

Clostridium perfringens epsilon toxin is associated with enterotoxaemia in livestock. More recently, it is proposed to play a role in multiple sclerosis (MS) in humans. Compared to matched controls, strains of C. perfringens which produce epsilon toxin are significantly more likely to be isolated from the gut of MS patients and at significantly higher levels; similarly, sera from MS patients are significantly more likely to contain antibodies to epsilon toxin. Epsilon toxin recognises the myelin and lymphocyte (MAL) protein receptor, damaging the blood-brain barrier and brain cells expressing MAL. In the experimental autoimmune encephalomyelitis model of MS, the toxin enables infiltration of immune cells into the central nervous system, inducing an MS-like disease. These studies provide evidence that epsilon toxin plays a role in MS, but do not yet fulfil Koch's postulates in proving a causal role.

Clostridium perfringens epsilon-toxin requires acid sphingomyelinase for cellular entry

OBJECTIVES

Clostridium perfringens epsilon-toxin is considered to be a crucial agent in enterotoxemia in domestic animals. Epsilon-toxin enters host cells via endocytosis and results in the formation of late endosome/lysosome-derived vacuoles. In the present study, we found that acid sphingomyelinase promotes the internalization of epsilon-toxin in MDCK cells.

METHODS

We measured the extracellular release of acid sphingomyelinase (ASMase) by epsilon-toxin. We examined the role of ASMase in epsilon-toxin-induced cytotoxicity using selective inhibitors and knockdown of ASMase. Production of ceramide after toxin treatment was determined by immunofluorescence technique.

RESULTS

Blocking agents of ASMase and exocytosis of lysosomes inhibited this epsilon-toxin-induced vacuole formation. Lysosomal ASMase was liberated to extracellular space during treatment of the cells with epsilon-toxin in the presence of Ca2+. RNAi-mediated attenuation of ASMase blocked epsilon-toxin-induced vacuolation. Moreover, incubation of MDCK cells with epsilon-toxin led to production of ceramide. The ceramide colocalized with lipid raft-binding cholera toxin subunit B (CTB) in the cell membrane, indicating that conversion of lipid raft associated sphingomyelin to ceramide by ASMase facilitates lesion of MDCK cells and internalization of epsilon-toxin.

CONCLUSIONS

Based on the present results, ASMase is required for efficient internalization of epsilon-toxin.

Clostridium perfringens Epsilon Toxin Binds to and Kills Primary Human Lymphocytes

Clostridium perfringens epsilon toxin (ETX) is the third most lethal bacterial toxin and has been suggested to be an environmental trigger of multiple sclerosis, an immune-mediated disease of the human central nervous system. However, ETX cytotoxicity on primary human cells has not been investigated. In this article, we demonstrate that ETX preferentially binds to and kills human lymphocytes expressing increased levels of the myelin and lymphocyte protein MAL. Using flow cytometry, ETX binding was determined to be time and dose dependent and was highest for CD4+ cells, followed by CD8+ and then CD19+ cells. Similar results were seen with ETX-induced cytotoxicity. To determine if ETX preference for CD4+ cells was related to MAL expression, MAL gene expression was determined by RT-qPCR. CD4+ cells had the highest amount of Mal gene expression followed by CD8+ and CD19+ cells. These data indicate that primary human cells are susceptible to ETX and support the hypothesis that MAL is a main receptor for ETX. Interestingly, ETX bindings to human lymphocytes suggest that ETX may influence immune response in multiple sclerosis.

Bacterial meningitis-induced demyelination: A logical fallacy or groundbreaking avenue in neuroscience?

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Epsilon toxin-producing Clostridium perfringens colonize the multiple sclerosis gut microbiome overcoming CNS immune privilege

Multiple sclerosis (MS) is a complex disease of the CNS thought to require an environmental trigger. Gut dysbiosis is common in MS, but specific causative species are unknown. To address this knowledge gap, we used sensitive and quantitative PCR detection to show that people with MS were more likely to harbor and show a greater abundance of epsilon toxin-producing (ETX-producing) strains of C. perfringens within their gut microbiomes compared with individuals who are healthy controls (HCs). Isolates derived from patients with MS produced functional ETX and had a genetic architecture typical of highly conjugative plasmids. In the active immunization model of experimental autoimmune encephalomyelitis (EAE), where pertussis toxin (PTX) is used to overcome CNS immune privilege, ETX can substitute for PTX. In contrast to PTX-induced EAE, where inflammatory demyelination is largely restricted to the spinal cord, ETX-induced EAE caused demyelination in the corpus callosum, thalamus, cerebellum, brainstem, and spinal cord, more akin to the neuroanatomical lesion distribution seen in MS. CNS endothelial cell transcriptional profiles revealed ETX-induced genes that are known to play a role in overcoming CNS immune privilege. Together, these findings suggest that ETX-producing C. perfringens strains are biologically plausible pathogens in MS that trigger inflammatory demyelination in the context of circulating myelin autoreactive lymphocytes.

Direct Visualization of the Dynamic Process of Epsilon Toxin on Hemolysis

Hemolysis is the process of rupturing erythrocytes (red blood cells) by forming nanopores on their membranes using hemolysins, which then impede membrane permeability. However, the self-assembly process before the state of transmembrane pores and underlying mechanisms of conformational change are not fully understood. In this work, theoretical and experimental evidence of the pre-pore morphology of Clostridium perfringens epsilon toxin (ETX), a typical hemolysin, is provided using in situ atomic force microscopy (AFM) complemented by molecular dynamics (MD) simulations to detect the conformational distribution of different states in Mica. The AFM suggests that the ETX pore is formed in two stages: ETX monomers first attach to the membrane and form a pre-pore in no special conditions required, which then undergo a conformational change to form a transmembrane pore at temperatures above the critical point in the presence of receptors. The authors' MD simulations reveal that initial nucleation occurs when specific amino acids adsorb to negatively charged mica cavities. This work fills the knowledge gap in understanding the early stage of hemolysis and the oligomerization of hemolysins. Moreover, the newly identified pre-pore of ETX holds promise as a candidate for nanopore applications.

Screening and Identification of DNA Nanostructure Aptamer Using the SELEX Method for ‎Detection of Epsilon Toxin

Background

Epsilon toxin (ETX), produced by Clostridium perfringens, is one of the most potent toxins known, with a lethal potency approaching that of botulinum neurotoxins. Epsilon toxin is responsible for enteritis. Therefore, the development of rapid and simple methods to detect ETX is imperative. Aptamers are single-stranded oligonucleotides that can bind tightly to specific target molecules with an affinity comparable to that of monoclonal antibodies (mAbs). DNA aptamers can serve as tools for the molecular identification of organisms, such as pathogen subspecies.

Objectives

This study aimed to isolate high-affinity single-stranded DNA (ssDNA) aptamers against ETX.

Methods

This study identified aptamers using the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) method, enzyme-linked apta-sorbent assay (ELASA), and surface plasmon resonance (SPR) to determine the affinity and specificity of the newly obtained aptamers targeting ETX.

Results

Several aptamers obtained through the SELEX process were studied. Among them, 2 aptamers, ETX clone 3 (ETX3; dissociation constant (Kd = 8.4 ± 2.4E-9M) and ETX11 (Kd = 6.3 ± 1.3E-9M) had favorable specificity for ETX. The limits of detection were 0.21 and 0.08 μg/mL for ETX3 and ETX11, respectively.‎.

Conclusions

The discovered aptamers can be used in various aptamer-based rapid diagnostic tests for the detection of ETX.

Pathology and Pathogenesis of Brain Lesions Produced by Clostridium perfringens Type D Epsilon Toxin

Clostridium perfringens type D epsilon toxin (ETX) produces severe, and frequently fatal, neurologic disease in ruminant livestock. The disorder is of worldwide distribution and, although vaccination has reduced its prevalence, ETX still causes substantial economic loss in livestock enterprises. The toxin is produced in the intestine as a relatively inactive prototoxin, which is subsequently fully enzymatically activated to ETX. When changed conditions in the intestinal milieu, particularly starch overload, favor rapid proliferation of this clostridial bacterium, large amounts of ETX can be elaborated. When sufficient toxin is absorbed from the intestine into the systemic circulation and reaches the brain, two neurologic syndromes can develop from this enterotoxemia. If the brain is exposed to large amounts of ETX, the lesions are fundamentally vasculocentric. The neurotoxin binds to microvascular endothelial receptors and other brain cells, the resulting damage causing increased vascular permeability and extravasation of plasma protein and abundant fluid into the brain parenchyma. While plasma protein, particularly albumin, pools largely perivascularly, the vasogenic edema becomes widely distributed in the brain, leading to a marked rise in intracranial pressure, coma, sometimes cerebellar herniation, and, eventually, often death. When smaller quantities of ETX are absorbed into the bloodstream, or livestock are partially immune, a more protracted clinical course ensues. The resulting brain injury is characterized by bilaterally symmetrical necrotic foci in certain selectively vulnerable neuroanatomic sites, termed focal symmetrical encephalomalacia. ETX has also been internationally listed as a potential bioterrorism agent. Although there are no confirmed human cases of ETX intoxication, the relatively wide species susceptibility to this toxin and its high toxicity mean it is likely that human populations would also be vulnerable to its neurotoxic actions. While the pathogenesis of ETX toxicity in the brain is incompletely understood, the putative mechanisms involved in neural lesion development are discussed.

Design of a chitosan-based nano vaccine against epsilon toxin of Clostridium perfringens type D and evaluation of its immunogenicity in BALB/c mice

Background and purpose

Clostridium perfringens is an anaerobic, spore-forming, and pathogenic bacterium that causes intestinal diseases in humans and animals. In these cases, therapeutic intervention is challenging; because the disease progresses much rapidly. This bacterium can produce 5 main toxins (alpha, beta, epsilon, iota, and a type of enterotoxin) among which the epsilon toxin (ETX) is used for bioterrorism. This toxin can be prevented by immunization with specific immunogenic vaccines. In the present research, we aimed at developing a recombinant chitosan-based nano-vaccine against ETX of C. perfringens and evaluate its effects on the antibody titration against epsilon toxin in BALB/c mice as the vaccine model.

Experimental approach

The etx gene from C. perfringens type D was cloned and expressed in E. coli. After analysis by SDS-PAGE and western blotting, the expressed products were purified, and the obtained proteins were used for immunization in mice as a chitosan nanoparticle containing recombinant, purified ETX, and protein.

Findings/Results

The results of ELISA showed that IgA antibody serum level increased sufficiently using recombinant protein with nanoparticle as an oral and injectable formulation. IgG antibody titers increased significantly after administrating the recombinant proteins with nanoparticles through both oral delivery and intravenous injection.

Conclusion and implication

In conclusion, the recombinant ETX is suggested as a good candidate for vaccine production against diseases caused by ETX of C. perfringens type D.

Molecular characterization of netB and tpeL virulence factors and antimicrobial resistance genes of Clostridium perfringens isolated from herbs and spices

The present study aimed to determine some virulence-associated genes and antimicrobial multidrug resistance of Clostridium perfringens recovered from herbs and spices widely distributed in the Egyptian market. C. perfringens virulence and resistance factors were determined using PCR targeting the netB, tpeL, ermB, bla and tetK genes. Thirty three out of 392 samples (8.42%) from herbs and spices submitted to our laboratory for bacteriological screening were positive for presence C. perfringens. PCR results for the tpeL gene in isolated C. perfringens revealed 9 out of 33 (27.3 %) of isolates, while netB was not detected. The isolates were resistant to Clindamycin, Vancomycin, tetracycline, and erythromycin with inhibition zones of 6.28 ± 0.63, 8.78 ± 0.41, 9.63 ± 0.63, and 9.84 ± 0.66 mm, respectively. The genes mentioned above were selected to correspond to the ineffective antimicrobials; ermB for erythromycin, tetK for tetracycline, and bla for the remainder. PCR results for antibacterial resistant genes in isolated C. perfringens revealed their presence. From 33 isolates, bla gene was detected in 21 (63.4 %), tetK in 13 (39.4 %) and ermB in only one isolate (3.03 %). Sequencing analysis was done for the bla gene as an example for the detected genes as detected at the highest incidence (63.4%). No cross-relationship was detected upon comparing incidence data of both studied virulence genes and those of antimicrobial resistance. The present findings may explain the resistance of C. perfringens to the examined antibacterials and recommend avoiding the application of them to control the microbe. In addition, the authors recommend following strict hygienic procedures during the industry of herbs and spices to ensure their clearance from Clostridium perfringens before distributing the products as food additives into the markets.

Investigation of genetic toxicity and oxidative stress of Clostridium perfringens epsilon toxin type D on human peripheral blood lymphocytes

Epsilon toxin (Etx) is an enormously potent pore-forming toxin and a category B biological agent. Etx is the main virulence determinant of Clostridiumperfringens types B and D toxin. It has a cytotoxic effect on distal and collecting kidney tubules. Also, Etx crosses the blood-brain barrier, binds to myelin structures, and destroys oligodendrocytes. The main purpose of this study was to investigate the toxic effects of Etx on human blood lymphocytes, which we examined for the first time for the genetic toxicity of this bacterial toxin. In this study, after taking blood and dividing into nine groups and putting in contact with different dilutions of Etx (1,5,10,25,50,100 and 200 μM), methotrexate (750 μM), and normal saline by Cytokinesis blocked micronucleus (CBMN) assay, we looked at genetic toxicity and the level of oxidative stress created in the under study lymphocytes. The results of this study showed that Etx has significant oxidative stress effects on human lymphocytes at doses above 25 μM, and also this bacterial toxin significantly increases the number of micronuclei formed in lymphocytes. The results of this study indicate that Etx has toxic effects it is genetic and interferes with cell division processes. Thus, human lymphocytes can be used extensively in future studies on Etx.

Production, immunogenicity, stability, and safety of a vaccine against Clostridium perfringens beta toxins

Background and Aim:

The beta toxin is causing the most severe Clostridium perfringens-related diseases. This work was dedicated to developing a vaccine against beta toxin using C. perfringens type C (NCTC 3180).

Materials and Methods:

The crude toxoid harvest contained 710 limits of flocculation (Lf)/mL. The vaccine was formulated. Each 1 mL of the final vaccine product contained at least 50 Lf/mL of beta toxoids, 0.2 mL 3% aluminum hydroxide gel (equivalent to 5.18 mg of aluminum), <0.001% W/V thiomersal, formaldehyde <0.05% W/V, and ~0.7 mL phosphate-buffered saline (pH 7.2). The efficacy of the vaccine was evaluated by potency, stability, and safety tests.

Results:

The vaccine demonstrated 24.36 IU/mL (standard deviation, ±0.56) and 14.74 IU/mL (±0.36) of neutralizing antibodies in rabbits and cattle, respectively. Indeed, these levels were above the minimum recommended by international protocols since the obtained antibody levels had 2.43- and 1.47-fold increase in both rabbits and cattle, respectively, over the minimum antitoxin level suggested by the United States Department of Agriculture. Interestingly, our formulation was capable of inducing 1.65-fold higher immune responses in rabbits than that stimulated in cattle (65% increase) with a significant difference (p<0.0001). The vaccine was stable up to 30 months. The vaccinated rabbits were suffered from a temporarily slight increase in temperatures in the first 10 h without any significant difference (p>0.05).

Conclusion:

The research showed a procedure for the manufacturing process of the vaccine against C. perfringens beta toxins with a feasible quantity and the vaccine described here showed to be effective in eliciting levels of neutralizing antibodies higher than required by international standards. In addition, The vaccine was stable up to 30 months. Thus, it may represent an effective and safe for preventing C. perfringens-related diseases in rabbits and cattle, although further studies to prove its efficacy in the field on other farm animals are still needed.

Prevalence, Genotypic and Phenotypic Characterization and Antibiotic Resistance Profile of Clostridium perfringens Type A and D Isolated from Feces of Sheep (Ovis aries) and Goats (Capra hircus) in Punjab, Pakistan

Clostridium perfringens poses a serious threat to small ruminants by causing moderate to severe enterotoxaemia. Due to its ability to produce a wide arsenal of toxins, it is ranked among the most prevalent and important pathogens in livestock. This study focused on the molecular characterization of different Clostridium perfringens types along with their antimicrobial resistance profile. An overall higher prevalence of C. perfringens (46.1%) was detected based on mPCR among sheep and goats (healthy and diseased) in the Punjab province, Pakistan. The majority of the isolates were characterized as type A (82%), followed by type D (18%). Among the isolates from diseased sheep and goats, 27% were positive for cpa, 49% for cpa and cpb2, 9% for cpa and etx, 15% for cpa, cpb2 and etx. In the case of isolates from healthy sheep and goats, 59% were positive for cpa, 34% for cpb2 and cpa, 4% for cpa and etx, and 3% for cpa, cpb2 and etx. The prevalence of the beta2 toxin gene in the diseased sheep and goat population was 64% as compared to 37% in healthy animals. All 184 isolates (100%) were sensitive to rifampin and ceftiofur; the majority (57%) was sensitive to teicoplanin, chloramphenicol, amoxicillin, linezolid and enrofloxacin. A lower proportion of isolates (43%) were sensitive to ciprofloxacin and only 14% were susceptible to erythromycin. The findings of this study highlight the higher prevalence of C. perfringens in small ruminants and indicate that detailed pathogenesis studies are necessary to understand the explicit role of various toxins in causing enteric infections in sheep and goats including how they might be exploited to develop vaccines against these diseases.

Isolation and Toxin Typing of Clostridium Perfringens From Sheep, Goats, and Cattle in Fars Province, Iran

Background: Clostridium perfringens is an important anaerobic bacterium found in the intestine of some livestock. It is concerned with the etiology of some diseases including enterotoxaemia. Various diseases are caused by different types of C. perfringens. Nonetheless, there is no published research on molecular typing and distribution of this pathogenic microorganism in Fars province. Objectives: Accordingly, our study focused on the isolation and toxin typing of C. perfringens from sheep, cattle, and goats in different parts of Fars province by the culture and the polymerase chain reaction (PCR) method. Materials and Methods: Approximately 459 fecal samples were collected and cultured on defined media for the isolation of C. perfringens. The confirmed isolates were genotyped by the PCR method using specific primers. Results: C. perfringens was isolated from 30.93% of the total samples. The results of toxin typing showed a total of 76 (54%), 13 (9%), 30 (21%), and 23 (16%) isolates as types A, B, C, and D, respectively. Conclusion: Our results indicated that C. perfringens type A was the most common type in sheep, cattle, and goats while the lowest number of isolates belonged to type B. Finally, the isolation of C. perfringens and toxin typing increase our knowledge of the epidemiology of these diseases and can help in the vaccine industry and better controlling related diseases.

Etx-Y71A as a non-toxic mutant of Clostridium perfringens epsilon toxin induces protective immunity in mice and sheep

Epsilon toxin (Etx) is an extremely potent toxin produced by Clostridium perfringens toxinotypes B and D, which cause fatal enterotoxemia in many livestock species, mainly sheep and goats. Our previous study demonstrated that the aromatic amino acid (AA) residue at position 71 in domain III of Etx is needed for its cytotoxic activity toward MDCK cells. Here, we first determined that Etx mutants with non-aromatic AA substitutions at Tyr71 lost lethality in mice, indicating that the aromatic AA residue at position 71 is a toxicity determinant of Etx in vivo. After intravenous injection with a high dose of the trypsin-activated Etx-Y71A mutant, mice did not show any histopathological lesions, and confocal microscopy observations further showed that Etx-Y71A lost the ability to cross the blood-brain barrier of the mice. These results suggested that the Etx-Y71A mutant is sufficiently safe in vivo to be a vaccine candidate. Furthermore, the immune efficacy of Etx-Y71A was evaluated in model and host animals. Mice inoculated with this mutant produced high levels of neutralizing antibodies and were completely protected from a 100 LD₅₀ of trypsin-activated Etx challenge. Sheep immunized with Etx-Y71A produced high levels of neutralizing antibodies that provided protection in mice against an activated Etx challenge, and lambs could receive passive immunity through immunization of pregnant ewes. Additionally, homology modeling and circular dichroism analysis showed that Etx-Y71A has structural similarity to Etx, which provides a structural basis for Etx-Y71A retaining the immunogenicity of Etx. Taken together, these results suggest that Etx-Y71A is a potential vaccine candidate against Etx-inducing enterotoxemia.

Insecticidal Activity of Bacillus thuringiensis Proteins Against Coleopteran Pests

Bacillus thuringiensis is the most successful microbial insecticide agent and its proteins have been studied for many years due to its toxicity against insects mainly belonging to the orders Lepidoptera, Diptera and Coleoptera, which are pests of agro-forestry and medical-veterinary interest. However, studies on the interactions between this bacterium and the insect species classified in the order Coleoptera are more limited when compared to other insect orders. To date, 45 Cry proteins, 2 Cyt proteins, 11 Vip proteins, and 2 Sip proteins have been reported with activity against coleopteran species. A number of these proteins have been successfully used in some insecticidal formulations and in the construction of transgenic crops to provide protection against main beetle pests. In this review, we provide an update on the activity of Bt toxins against coleopteran insects, as well as specific information about the structure and mode of action of coleopteran Bt proteins.

Clostridium perfringens epsilon toxin binds to erythrocyte MAL receptors and triggers phosphatidylserine exposure

Epsilon toxin (ETX) is a 33-kDa pore-forming toxin produced by type B and D strains of Clostridium perfringens. We previously found that ETX caused haemolysis of human red blood cells, but not of erythrocytes from other species. The cellular and molecular mechanisms of ETX-mediated haemolysis are not well understood. Here, we investigated the effects of ETX on erythrocyte volume and the role of the putative myelin and lymphocyte (MAL) receptors in ETX-mediated haemolysis. We observed that ETX initially decreased erythrocyte size, followed by a gradual increase in volume until lysis. Moreover, ETX triggered phosphatidylserine (PS) exposure and enhanced ceramide abundance in erythrocytes. Cell shrinkage, PS exposure and enhanced ceramide abundance were preceded by increases in intracellular Ca²⁺ concentration. Interestingly, lentivirus-mediated RNA interference studies in the human erythroleukaemia cell line (HEL) cells confirmed that MAL contributes to ETX-induced cytotoxicity. Additionally, ETX was shown to bind to MAL in vitro. The results of this study recommend that ETX-mediated haemolysis is associated with MAL receptor activation in human erythrocytes. These data imply that interventions affecting local MAL-mediated autocrine and paracrine signalling may prevent ETX-mediated erythrocyte damage.

Putative serum protein biomarkers for epsilon toxin exposure in mouse model using LC-MS/MS analysis

Epsilon toxin (ETX), produced by Clostridium perfringens Type B or type D strains, is a potential biological and toxin warfare (BTW) agent, largely for its very high toxicity. The toxin is implicated in several animal diseases. Using LC-MS/MS analysis, we report here elucidation of putative serum maker proteins for ETX exposure with an objective of the early diagnosis of intoxication. Of 166 consensus proteins (488 peptides), showing ETX-induced alterations, 119 proteins exhibited increase and 47 proteins showed decreased abundance in serum, as revealed by SWATH (DIA) acquisition on LC-MS/MS and label free quantitative analysis of control and test samples. Complement and coagulation cascade, nitrogen metabolism, negative regulation of peptidase activity, and response to ROS were among the biological processes and pathways perturbed by the ETX exposure. Interaction network indicated enzyme inhibitor activity, detoxification of ROS, and steroid binding functions were the major interaction networks for the proteins with increased abundance, while, hemostasis and structural molecule activity were the prominent networks for the down-regulated proteins. Validation studies were carried out by immunoprecipitation, ELISA, and Western blot analysis of selected proteins to demonstrate diagnostic potential of the putative marker proteins of ETX exposure.

Clostridium perfringens Epsilon-Toxin Impairs the Barrier Function in MDCK Cell Monolayers in a Ca2+-Dependent Manner

Epsilon-toxin produced by Clostridium perfringens significantly contributes to the pathogeneses of enterotoxemia in ruminants and multiple sclerosis in humans. Epsilon-toxin forms a heptameric oligomer in the host cell membrane, promoting cell disruption. Here, we investigate the effect of epsilon-toxin on epithelial barrier functions. Epsilon-toxin impairs the barrier integrity of Madin-Darby Canine Kidney (MDCK) cells, as demonstrated by decreased transepithelial electrical resistance (TEER), increased paracellular flux marker permeability, and the decreased cellular localization of junctional proteins, such as occludin, ZO-1, and claudin-1. U73122, an endogenous phospholipase C (PLC) inhibitor, inhibited the decrease in TEER and the increase in the permeability of flux marker induced by epsilon-toxin. The application of epsilon-toxin to MDCK cells resulted in the biphasic formation of 1,2-diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP₃). U73122 blocked the formation of DAG and IP₃ induced by the toxin. Epsilon-toxin also specifically activated endogenous PLC-γ1. Epsilon-toxin dose-dependently increased the cytosolic calcium ion concentration ([Ca²⁺]i). The toxin-induced elevation of [Ca²⁺]i was inhibited by U73122. Cofilin is a key regulator of actin cytoskeleton turnover and tight-junction (TJ) permeability regulation. Epsilon-toxin caused cofilin dephosphorylation. These results demonstrate that epsilon-toxin induces Ca²⁺ influx through activating the phosphorylation of PLC-γ1 and then causes TJ opening accompanied by cofilin dephosphorylation.

In vitro characterization and immunogenicity of chitosan nanoparticles loaded with native and inactivated extracellular proteins from a field strain of Clostridium perfringens associated with necrotic enteritis

There are currently no licensed vaccines against Clostridium perfringens which causes necrotic enteritis in poultry. Chitosan nanoparticles were formulated with native (CN) or toxoids (CT) of extracellular proteins (ECP) of C. perfringens, both surface-tagged with Salmonella flagellar proteins. In a pH stability assay, CN and CT nanoparticles released 6% and 0% of their protein at 8.0 pH. In a protein release assay, CN and CT nanoparticles released 16% and 10% of their protein respectively at 7.4 pH after 24 h. CN and CT nanoparticles incubated at 100 μg/mL PBS with Chicken RBCs released 1% and 0% hemoglobin respectively. Ninety broilers were randomly assigned to treatments; sham-vaccinated (Control), CN-vaccinated (CN), and CT-vaccinated (CT). Each bird was orally gavaged with 50 μg vaccine in 0.5 mL PBS or 0.5 mL PBS only on d 0, 3, 7 and 14 of age. At 21 d of age, the CN group had higher anti-ECP IgA than control (P < 0.05). At 21 d of age, the CN and CT group had higher anti-ECP IgA than control (P < 0.05). At 17 d of age, the CN group had higher anti-flagellar IgG than control (P < 0.05). At 10 d of age, the CN group had higher anti-flagellar IgA than control (P < 0.05). Splenic T cells from chickens in the CN and CT group ex-vivo stimulated with 0.05 mg/mL ECP, had higher proliferation control (P < 0.05, P < 0.01 respectively). Splenic T cells from chickens in the CN and CT groups ex-vivo stimulated with 0.1 mg/mL ECP had proliferation than control (P < 0.05). Pooled serum from 17 d of age CN and CT-vaccinated birds partially neutralized toxins in 50 μg of ECP (P < 0.05). Pooled serum from 28 d of age CN-vaccinated birds also partially neutralized toxins in 50 μg of ECP. The result from this study indicates the potential for chitosan loaded with Clostridium perfringens extracellular proteins to be applied to necrotic enteritis challenge studies.

Research Note: Effect of synbiotic supplementation on caecal Clostridium perfringens load in broiler chickens with different necrotic enteritis challenge models

Studies were conducted to determine the efficacy of synbiotic applications to combat the negative effects of necrotic enteritis (NE). An in vitro study was conducted to test the effect of probiotics species supernatants to decrease Clostridium perfringens (CP) proliferation. Lactobacillus reuteri, Enterococcus faecium, Bifidobacterium animalis, and Pediococcus acidilactici culture supernatants decreased the proliferation of CP at 1:1 supernatant-to-pathogen dilution in vitro. Two in vivo studies were conducted to determine the in vivo response of synbiotic supplementation containing the aforementioned probiotic strains on broiler production performance and caecal CP load in broilers induced with NE infection. In experiment 1, 75 broiler chicks were randomly allotted to 3 treatment groups, control (basal diet), ionophore (Salinomycin), and synbiotic (PoultryStar me), from day of hatch, and NE was induced in all birds. There were no significant treatment effects on BW, feed consumption, and feed gain ratio. However, at 35 D, ionophore or synbiotic supplementation increased (P < 0.05) villi height and decreased interleukin (IL)-1 mRNA abundance, while synbiotic supplementation increased (P < 0.05) IL-10 mRNA abundance compared with the control group, respectively. In experiment 2, 360 broiler chicks were randomly allotted to 3 treatments, an unchallenged negative control (control; basal diet), challenged positive control (NE; basal diet), or NE + synbiotic group (synbiotic). At both 21 and 42 D of age, NE birds had decreased (P < 0.05) BW, feed conversion, and jejunal villi height compared with control, while NE + synbiotic birds were not different from control groups. At 42 D of age, NE birds had 2.2 log/g increased CP in the ceca contents compared with control, while synbiotic birds had CP load that was not different than that of the control group. NE + synbiotic birds had significantly greater amounts of bile anti-CP IgA than the control and NE groups. It can be concluded that synbiotic supplementation decreased CP proliferation in vitro and caecal CP load in vivo while improving production parameters during an NE infection in broilers.

Bacillus thuringiensis novel toxin Epp is toxic to mosquitoes and prodenia litura larvae

As a pathogenic bacterium, Bacillus thuringiensis (Bt) has become an alternative to chemical insecticides in commercial agricultural to control forestry pests and mosquitoes. To prevent pest resistance, many novel Bt strains have been isolated. Strain S3580-1 (WGS: VHPX0000000) used in this research and originally isolated from Hainan Qixianling National Forest Park (China) showed significant toxicity to Culex pipiens pallens. Here, using whole genome sequencing, assembly, and bioinformatics analysis, the predicted S3580-1CG_5163 (GenBank Accession No. MK124137) gene-encoded protein was found to share low homology with known toxins designated by the Bt toxin nomenclature system. It was considered to be an ETX/MTX2-type toxin and was designated Epp. Bioinformatics analysis showed that the predicted S3580-1CG_5163 gene-encoded protein Epp shared low identity with other known toxic protein sequences containing Cry-ETX/MTX conserved domains at the amino acid level, but significant similarity at the structural level. In addition, bioassays showed that Epp was toxic against Spodoptera litura (LC₅₀ 296.133 μg/mL; 95% FL 200.555-471.318 μg/mL) and Cx. pipiens pallens (LC₅₀ 322.193 μg/mL; 95% FL 238.217-477.243 μg/mL). On pathological observation, the peritrophic membrane of Cx. pipiens pallens larvae was degraded causing the midgut structure to become incomplete, resulting in larval death. Further bioassays are required to fully elucidate the insecticidal spectrum of the ETX/MTX2-type toxin Epp, and thereby provide future research directions.

Clostridium perfringens epsilon toxin induces blood brain barrier permeability via caveolae-dependent transcytosis and requires expression of MAL

Clostridium perfringens epsilon toxin (ETX) is responsible for causing the economically devastating disease, enterotoxaemia, in livestock. It is well accepted that ETX causes blood brain barrier (BBB) permeability, however the mechanisms involved in this process are not well understood. Using in vivo and in vitro methods, we determined that ETX causes BBB permeability in mice by increasing caveolae-dependent transcytosis in brain endothelial cells. When mice are intravenously injected with ETX, robust ETX binding is observed in the microvasculature of the central nervous system (CNS) with limited to no binding observed in the vasculature of peripheral organs, indicating that ETX specifically targets CNS endothelial cells. ETX binding to CNS microvasculature is dependent on MAL expression, as ETX binding to CNS microvasculature of MAL-deficient mice was not detected. ETX treatment also induces extravasation of molecular tracers including 376Da fluorescein salt, 60kDA serum albumin, 70kDa dextran, and 155kDA IgG. Importantly, ETX-induced BBB permeability requires expression of both MAL and caveolin-1, as mice deficient in MAL or caveolin-1 did not exhibit ETX-induced BBB permeability. Examination of primary murine brain endothelial cells revealed an increase in caveolae in ETX-treated cells, resulting in dynamin and lipid raft-dependent vacuolation without cell death. ETX-treatment also results in a rapid loss of EEA1 positive early endosomes and accumulation of large, RAB7-positive late endosomes and multivesicular bodies. Based on these results, we hypothesize that ETX binds to MAL on the apical surface of brain endothelial cells, causing recruitment of caveolin-1, triggering caveolae formation and internalization. Internalized caveolae fuse with early endosomes which traffic to late endosomes and multivesicular bodies. We believe that these multivesicular bodies fuse basally, releasing their contents into the brain parenchyma.

Clostridium perfringens epsilon toxin (ETX) is an extremely lethal bacterial toxin known to cause a devastating disease in livestock animals and may be a possible cause of multiple sclerosis in humans. ETX is well known to cause disruption of the blood-brain barrier (BBB), a critical structure necessary for proper brain function. Deterioration of this barrier allows entry of toxic blood-borne material to enter the brain. Although ETX-induced BBB dysfunction is well accepted, how this happens is unknown. Here, we demonstrate that ETX causes BBB permeability by inducing formation of cell-surface invaginations called caveolae in endothelial cells, the cells that line blood vessels. Importantly, only endothelial cells from the brain and other central nervous system organs appear to be a target of ETX, as the toxin only binds to blood vessels in these organs and not blood vessels from other organs. These ETX-induced caveolae fuse with other caveolae and specialized intracellular vesicles called endosomes. We predict that these endosomes engulf blood-borne material during their internalization, allowing material to travel from the blood, through the cell, and into brain tissue. We also show that expression of the protein MAL and caveolin-1 is necessary for ETX-induced BBB permeability.

The First Identification and Antibiogram of Clostridium perfringens Type C Isolated from Soil and The Feces of Dead Foals in South Korea

Clostridium (C.) perfringens was isolated from 25 (11.1%) of 225 sampled horses and from 16 (35.56%) of 45 farms. All of the samples were negative for cpe, etx, itx, NetF genes and cpa gene were detected in 100% (25 of 25) of the samples that were positive for C. perfringens. cpb and cpb2 were detected in 40.0% (10 of 25) and 60.0% (15 of 25) of the samples that were positive for C. perfringens, respectively. Of the 25 C. perfringens isolates, 15 (60%) were type A and 10 (40%) were type C. Type C was observed on all the farms where the foals' deaths occurred. None of the isolates were positive for type B, type D, or type E. The MIC Evaluator strips antimicrobial susceptibility test showed meropenem (96%), ampicillin (92%), amoxicillin/clavulanic acid (84%), and tetracycline (8%) sensitivity.

Clostridium perfringens epsilon toxin vaccine candidate lacking toxicity to cells expressing myelin and lymphocyte protein

A variant form of Clostridium perfringens epsilon toxin (Y30A-Y196A) with mutations, which shows reduced binding to Madin–Darby canine kidney (MDCK) cells and reduced toxicity in mice, has been proposed as the next-generation enterotoxaemia vaccine. Here we show that, unexpectedly, the Y30A-Y196A variant does not show a reduction in toxicity towards Chinese hamster ovary (CHO) cells engineered to express the putative receptor for the toxin (myelin and lymphocyte protein; MAL). The further addition of mutations to residues in a second putative receptor binding site of the Y30A-Y196A variant further reduces toxicity, and we selected Y30A-Y196A-A168F for further study. Compared to Y30A-Y196A, Y30A-Y196A-A168F showed more than a 3-fold reduction in toxicity towards MDCK cells, more than a 4-fold reduction in toxicity towards mice and at least 200-fold reduction in toxicity towards CHO cells expressing sheep MAL. The immunisation of rabbits or sheep with Y30A-Y196A-A168F induced high levels of neutralising antibodies against epsilon toxin, which persisted for at least 1 year. Y30A-Y196A-A168F is a candidate for development as a next-generation enterotoxaemia vaccine.

Cells expressing myelin and lymphocyte protein (MAL), the putative receptor for Clostridium perfringens’ epsilon toxin, can be sensitive to otherwise attenuated mutants of the toxin. Here, the team led by Richard Titball at United Kingdom’s University of Exeter found that a previous variant exhibits differential toxic effects when cells express sheep or human MAL. To circumvent this, Titball’s team applied site-directed mutagenesis of the receptor binding site to develop a new variant with enhanced reduction in toxicity towards MAL-expressing cells and able to induce high levels of neutralising antibodies upon immunisation of sheep. These findings suggests that testing genetic toxoids in cells expressing MAL from the target species might be relevant for enterotoxaemia vaccine development and warrant further studies into the role of MAL in epsilon toxin-mediated pathogenesis.

The pore structure of Clostridium perfringens epsilon toxin

Epsilon toxin (Etx), a potent pore forming toxin (PFT) produced by Clostridium perfringens, is responsible for the pathogenesis of enterotoxaemia of ruminants and has been suggested to play a role in multiple sclerosis in humans. Etx is a member of the aerolysin family of β-PFTs (aβ-PFTs). While the Etx soluble monomer structure was solved in 2004, Etx pore structure has remained elusive due to the difficulty of isolating the pore complex. Here we show the cryo-electron microscopy structure of Etx pore assembled on the membrane of susceptible cells. The pore structure explains important mutant phenotypes and suggests that the double β-barrel, a common feature of the aβ-PFTs, may be an important structural element in driving efficient pore formation. These insights provide the framework for the development of novel therapeutics to prevent human and animal infections, and are relevant for nano-biotechnology applications.

Epsilon toxin (Etx) is a potent pore forming toxin (PFT) produced by Clostridium perfringens. Here authors show the cryo-EM structure of the Etx pore assembled on the membrane of susceptible cells and shed light on pore formation and mutant phenotypes.

Clostridium perfringens Epsilon Toxin Compromises the Blood-Brain Barrier in a Humanized Zebrafish Model

Clostridium perfringens epsilon toxin (ETX) is hypothesized to mediate blood-brain barrier (BBB) permeability by binding to the myelin and lymphocyte protein (MAL) on the luminal surface of endothelial cells (ECs). However, the kinetics of this interaction and a general understanding of ETX's behavior in a live organism have yet to be appreciated. Here we investigate ETX binding and BBB breakdown in living Danio rerio (zebrafish). Wild-type zebrafish ECs do not bind ETX. When zebrafish ECs are engineered to express human MAL (hMAL), proETX binding occurs in a time-dependent manner. Injection of activated toxin in hMAL zebrafish initiates BBB leakage, hMAL downregulation, blood vessel stenosis, perivascular edema, and blood stasis. We propose a kinetic model of MAL-dependent ETX binding and neurovascular pathology. By generating a humanized zebrafish BBB model, this study contributes to our understanding of ETX-induced BBB permeability and strengthens the proposal that MAL is the ETX receptor.

Elucidation of protein biomarkers in plasma and urine for epsilon toxin exposure in mouse model

Epsilon toxin (ETX) is the major virulence determinant of C. perfringens type B or type D strains, causing diseases in animals, besides being a listed biological and toxin warfare (BTW) agent. Keeping in mind the high lethality and the rapid onset of clinical manifestations, early diagnosis of epsilon toxin exposure is of paramount importance for implementation of appropriate medical countermeasures. Using a 2DE-MS approach, the present study is the first comprehensive proteomic elucidation of ETX-induced protein markers in the mouse model, providing putative targets for early diagnosis of ETX exposure. A total of 52 unique proteins showing ETX-induced modulations were identified in plasma and urine samples. Fibrinogen, apolipoprotein, serum amyloid protein, plasminogen, serum albumin, glutathione peroxidase, transferrin, major urinary protein 2, haptoglobin, transthyretin, and vitamin D-binding protein were among the proteins observed in more than one dataset with altered abundance after the ETX-intoxication. The predicted localization, function, and interaction of the ETX-modulated proteins in the plasma and urine indicated involvement of multiple pathways; extracellular proteins, followed by macromolecular complexes associated with blood coagulation and plasminogen activating cascade, being the most prominent among others. The putative markers elucidated here warrants further validation and can be of immense value for the early diagnosis of ETX exposure.

Research articleHemolysis in human erythrocytes by Clostridium perfringens epsilon toxin requires activation of P2 receptors

Epsilon-toxin (ETX) is produced by types B and D strains of Clostridium perfringens, which cause fatal enterotoxaemia in sheep, goats and cattle. Previous studies showed that only a restricted number of cell lines are sensitive to ETX and ETX-induced hemolysis has not previously been reported. In this study, the hemolytic ability of ETX was examined using erythrocytes from 10 species including murine, rabbit, sheep, monkey and human. We found that ETX caused hemolysis in human erythrocytes (HC₅₀ = 0.2 μM) but not erythrocytes from the other test species. Moreover, the mechanism of ETX-induced hemolysis was further explored. Recent studies showed that some bacterial toxins induce hemolysis through purinergic receptor (P2) activation. Hence, the function of purinergic receptors in ETX-induced hemolysis was tested, and we found that the non-selective P2 receptor antagonists PPADS inhibited ETX-induced lysis of human erythrocytes in a concentration-dependent manner, indicating that ETX-induced hemolysis requires activation of purinergic receptors. P2 receptors comprise seven P2X (P2X1-7) and eight P2Y (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11-P2Y14) receptor subtypes. The pattern of responsiveness to more selective P2-antagonists implies that both P2Y13 and P2X7 receptors are involved in ETX-induced hemolysis in human species. Furthermore, we demonstrated that extracellular ATP is likely not involved in ETX-induced hemolysis and the activation of P2 receptors. These findings clarified the mechanism of ETX-induced hemolysis and provided new insight into the activities and ETX mode of action.

A Novel Panel of Rabbit Monoclonal Antibodies and Their Diverse Applications Including Inhibition of Clostridium perfringens Epsilon Toxin Oligomerization

The pore-forming epsilon toxin (ETX) produced by Clostridium perfringens is among the most lethal bacterial toxins known. Sensitive antibody-based reagents are needed to detect toxin, distinguish mechanisms of cell death, and prevent ETX toxicity. Using B-cell immuno-panning and cloning techniques, seven ETX-specific monoclonal antibodies were generated from immunized rabbits. ETX specificity and sensitivity were evaluated via western blot, ELISA, immunocytochemistry (ICC), and flow cytometry. ETX-neutralizing function was evaluated both in vitro and in vivo. All antibodies recognized both purified ETX and epsilon protoxin via western blot with two capable of detecting the ETX-oligomer complex. Four antibodies detected ETX via ELISA and three detected ETX bound to cells via ICC or flow cytometry. Several antibodies prevented ETX-induced cell death by either preventing ETX binding or by blocking ETX oligomerization. Antibodies that blocked ETX oligomerization inhibited ETX endocytosis and cellular vacuolation. Importantly, one of the oligomerization-blocking antibodies was able to protect against ETX-induced death post-ETX exposure in vitro and in vivo. Here we describe the production of a panel of rabbit monoclonal anti-ETX antibodies and their use in various biological assays. Antibodies possessing differential specificity to ETX in particular conformations will aid in the mechanistic studies of ETX cytotoxicity, while those with ETX-neutralizing function may be useful in preventing ETX-mediated mortality.

Clostridium perfringens Enterotoxin: The Toxin Forms Highly Cation-Selective Channels in Lipid Bilayers

One of the numerous toxins produced by Clostridium perfringens is Clostridium perfringens enterotoxin (CPE), a polypeptide with a molecular mass of 35.5 kDa exhibiting three different domains. Domain one is responsible for receptor binding, domain two is involved in hexamer formation and domain three has to do with channel formation in membranes. CPE is the major virulence factor of this bacterium and acts on the claudin-receptor containing tight junctions between epithelial cells resulting in various gastrointestinal diseases. The activity of CPE on Vero cells was demonstrated by the entry of propidium iodide (PI) in the cells. The entry of propidium iodide caused by CPE was well correlated with the loss of cell viability monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test. CPE formed ion-permeable channels in artificial lipid bilayer membranes with a single-channel conductance of 620 pS in 1 M KCl. The single-channel conductance was not a linear function of the bulk aqueous salt concentration indicating that point-negative charges at the CPE channel controlled ion transport. This resulted in the high cation selectivity of the CPE channels, which suggested that anions are presumably not permeable through the CPE channels. The possible role of cation transport by CPE channels in disease caused by C. perfringens is discussed.

Epsilon toxin from Clostridium perfringens induces cytotoxicity in FRT thyroid epithelial cells

Epsilon toxin (Etx) is produced by Clostridium perfringens and induces enterotoxemia in ruminants. Etx crosses the blood-brain barrier, binds to myelin structures, and kills oligodendrocytes, inducing central nervous system demyelination. In addition, Etx has a cytotoxic effect on distal and collecting kidney tubules. There are few cell lines sensitive to Etx. At present, the most sensitive in vitro model for Etx is the Madin-Darby canine kidney (MDCK) cell line, where Etx oligomerizes and forms a pore with consequent ion efflux and cell death. Although the Etx receptor has not yet been fully clarified, it is known that caveolin 1 and 2 potentiate Etx cytotoxicity and oligomerization, and more recently, the myelin and lymphocyte (MAL) protein has been implicated in Etx binding and activity. Here, we studied the effect of Etx on Fischer rat thyroid cells (FRT) and observed similar effects as those seen in MDCK cells. Etx incubated with FRT cells showed binding to the plasma membrane, and western blotting assays revealed oligomeric complex formation. Moreover, cytotoxic assays on FRT cells after Etx incubation indicated cell death at a similar level as in MDCK cells. In addition, a luminescent ATP detection assay revealed ATP depletion in FRT cells after Etx exposure. Previous studies have reported that FRT cells do not express caveolins and do not form caveolae but express MAL protein in glycolipid-enriched membrane microdomains. Our results indicate that caveolins are not directly implicated in Etx cytotoxicity, supporting the notion that the MAL protein is involved in Etx action. In addition, a cell line of thyroid origin is described for the first time as a good model to study Etx action.

Mechanisms of Action and Cell Death Associated with Clostridium perfringens Toxins

Clostridium perfringens uses its large arsenal of protein toxins to produce histotoxic, neurologic and intestinal infections in humans and animals. The major toxins involved in diseases are alpha (CPA), beta (CPB), epsilon (ETX), iota (ITX), enterotoxin (CPE), and necrotic B-like (NetB) toxins. CPA is the main virulence factor involved in gas gangrene in humans, whereas its role in animal diseases is limited and controversial. CPB is responsible for necrotizing enteritis and enterotoxemia, mostly in neonatal individuals of many animal species, including humans. ETX is the main toxin involved in enterotoxemia of sheep and goats. ITX has been implicated in cases of enteritis in rabbits and other animal species; however, its specific role in causing disease has not been proved. CPE is responsible for human food-poisoning and non-foodborne C. perfringens-mediated diarrhea. NetB is the cause of necrotic enteritis in chickens. In most cases, host–toxin interaction starts on the plasma membrane of target cells via specific receptors, resulting in the activation of intracellular pathways with a variety of effects, commonly including cell death. In general, the molecular mechanisms of cell death associated with C. perfringens toxins involve features of apoptosis, necrosis and/or necroptosis.

Evidence of Clostridium perfringens epsilon toxin associated with multiple sclerosis

Background:

It was recently reported that, using Western blotting, some multiple sclerosis (MS) patients in the United States had antibodies against epsilon toxin (Etx) from Clostridium perfringens, suggesting that the toxin may play a role in the disease.

Objective:

We investigated for serum antibodies against Etx in UK patients with clinically definite multiple sclerosis (CDMS) or presenting with clinically isolated syndrome (CIS) or optic neuritis (ON) and in age- and gender-matched controls.

Methods:

We tested sera from CDMS, CIS or ON patients or controls by Western blotting. We also tested CDMS sera for reactivity with linear overlapping peptides spanning the amino acid sequence (Pepscan) of Etx.

Results:

Using Western blotting, 24% of sera in the combined CDMS, CIS and ON groups (n = 125) reacted with Etx. In the control group (n = 125), 10% of the samples reacted. Using Pepscan, 33% of sera tested reacted with at least one peptide, whereas in the control group only 16% of sera reacted. Out of 61 samples, 21 (43%) were positive to one or other testing methodology. Three samples were positive by Western blotting and Pepscan.

Conclusion:

Our results broadly support the previous findings and the role of Etx in the aetiology of MS warrants further investigation.

Cry64Ba and Cry64Ca, Two ETX/MTX2-Type Bacillus thuringiensis Insecticidal Proteins Active against Hemipteran Pests

Genetically modified crops that express insecticidal Bacillus thuringiensis (Bt) proteins have become a primary approach for control of lepidopteran (moth) and coleopteran (beetle) pests that feed by chewing the plants. However, the sap-sucking insects (Hemiptera) are not particularly susceptible to Bt toxins. In this study, we describe two Cry toxins (Cry64Ba and Cry64Ca) from Bt strain 1012 that showed toxicity against two important hemipteran rice pests, Laodelphax striatellus and Sogatella furcifera Both of these proteins contain an ETX/MTX2 domain and share common sequence features with the β-pore-forming toxins. Coexpression of cry64Ba and cry64Ca genes in the acrystalliferous Bt strain HD73^- resulted in high insecticidal activity against both hemipteran pests. No toxicity was observed on other pests such as Ostrinia furnacalis, Plutella xylostella, or Colaphellus bowringi Also, no hemolytic activity or toxicity against cancer cells was detected. Binding assays showed specific binding of the Cry64Ba/Cry64Ca toxin complex to brush border membrane vesicles isolated from L. striatellus Cry64Ba and Cry64Ca are Bt Cry toxins highly effective against hemipteran pests and could provide a novel strategy for the environmentally friendly biological control of rice planthoppers in transgenic plants.IMPORTANCE In Asia, rice is an important staple food, whose production is threatened by rice planthoppers. To date, no effective Bacillus thuringiensis (Bt) protein has been shown to have activity against rice planthoppers. We cloned two Bt toxin genes from Bt strain 1012 that showed toxicity against small brown planthoppers (Laodelphax striatellus) and white-backed planthoppers (Sogatella furcifera). To our knowledge, the proteins encoded by the cry64Ba and cry64Ca genes are the most efficient insecticidal Bt Cry proteins with activity against hemipteran insects reported so far. Cry64Ba and Cry64Ca showed no toxicity against some lepidopteran or coleopteran pests. These two proteins should be able to be used for integrated hemipteran pest management.

Acute Effect of Pore-Forming Clostridium perfringens ε-Toxin on Compound Action Potentials of Optic Nerve of Mouse

ε-Toxin is a pore forming toxin produced by Clostridium perfringens types B and D. It is synthesized as a less active prototoxin form that becomes fully active upon proteolytic activation. The toxin produces highly lethal enterotoxaemia in ruminants, has the ability to cross the blood–brain barrier (BBB) and specifically binds to myelinated fibers. We discovered that the toxin induced a release of ATP from isolated mice optic nerves, which are composed of myelinated fibers that are extended from the central nervous system. We also investigated the effect of the toxin on compound action potentials (CAPs) in isolated mice optic nerves. When nerves were stimulated at 100 Hz during 200 ms, the decrease of the amplitude and the area of the CAPs was attenuated in the presence of ε-toxin. The computational modelling of myelinated fibers of mouse optic nerve revealed that the experimental results can be mimicked by an increase of the conductance of myelin and agrees with the pore forming activity of the toxin which binds to myelin and could drill it by making pores. The intimate ultrastructure of myelin was not modified during the periods of time investigated. In summary, the acute action of the toxin produces a subtle functional impact on the propagation of the nerve action potential in myelinated fibers of the central nervous system with an eventual desynchronization of the information. These results may agree with the hypothesis that the toxin could be an environmental trigger of multiple sclerosis (MS).

Highly sensitive sandwich immunoassay and immunochromatographic test for the detection of Clostridial epsilon toxin in complex matrices

Epsilon toxin is one of the four major toxins of Clostridium perfringens. It is the third most potent clostridial toxin after botulinum and tetanus toxins and is thus considered as a potential biological weapon classified as category B by the Centers for Disease Control and Prevention (CDC). In the case of a bioterrorist attack, there will be a need for a rapid, sensitive and specific detection method to monitor food and water contamination by this toxin, and for a simple human diagnostic test. We have produced and characterized five monoclonal antibodies against common epitopes of epsilon toxin and prototoxin. Three of them neutralize the cytotoxic effects of epsilon toxin in vitro. With these antibodies, we have developed highly sensitive tests, overnight and 4-h sandwich enzyme immunoassays and an immunochromatographic test performed in 20 min, reaching detection limits of at least 5 pg/mL (0.15 pM), 30 pg/mL (0.9 pM) and 100 pg/mL (3.5 pM) in buffer, respectively. These tests were also evaluated for detection of epsilon toxin in different matrices: milk and tap water for biological threat detection, serum, stool and intestinal content for human or veterinary diagnostic purposes. Detection limits in these complex matrices were at least 5-fold better than those described in the literature (around 1 to 5 ng/mL), reaching 10 to 300 pg/mL using the enzyme immunoassay and 100 to 2000 pg/mL using the immunochromatographic test.

The Contribution of Bacteriophages to the Biology and Virulence of Pathogenic Clostridia

Bacteriophages are key players in the evolution of most bacteria. Temperate phages have been associated with virulence of some of the deadliest pathogenic bacteria. Among the most notorious cases, the genes encoding the botulinum neurotoxin produced by Clostridium botulinum types C and D and the α-toxin (TcnA) produced by Clostridium novyi are both encoded within prophage genomes. Clostridium difficile is another important human pathogen and the recent identification of a complete binary toxin locus (CdtLoc) carried on a C. difficile prophage raises the potential for horizontal transfer of toxin genes by mobile genetic elements. Although the TcdA and TcdB toxins produced by C. difficile have never been found outside the pathogenicity locus (PaLoc), some prophages can still influence their production. Prophages can alter the expression of several metabolic and regulatory genes in C. difficile, as well as cell surface proteins such as CwpV, which confers phage resistance. Homologs of an Agr-like quorum sensing system have been identified in a C. difficile prophage, suggesting that it could possibly participate in cell-cell communication. Yet, other C. difficile prophages contain riboswitches predicted to recognize the secondary messenger molecule c-di-GMP involved in bacterial multicellular behaviors. Altogether, recent findings on clostridial phages underline the diversity of mechanisms and intricate relationship linking phages with their host. Here, milestone discoveries linking phages and virulence of some of the most pathogenic clostridial species will be retraced, with a focus on C. botulinum, C. novyi, C. difficile, and Clostridium perfringens phages, for which evidences are mostly available.

Evaluation of plant-produced <i>Clostridium perfringens</i> type D <i>epsilon</i> toxoid in a vaccine against enterotoxaemia in sheep

Enterotoxaemia (pulpy kidney) is a common bacterial disease of sheep caused by Clostridium perfringens type D epsilon toxin. It has mortality rates of up to 30% in non-vaccinated animals. Current vaccines from whole cell cultures are expensive to manufacture and can induce local inflammatory responses in sheep. They usually have reduced immunogenicity because of the difficulty of standardising the inactivation step in vaccine manufacturing. In the current study, we evaluated the safety and potency of a recombinant plant-made epsilon toxoid protein (r-Etox) as an affordable and safer alternative vaccine for developing countries. Results of injection site reactions, rectal temperature and toxin neutralisation test in single and prime–boost inoculations of mice, guinea pigs and sheep suggest that the product is not toxic to animals and could protect sheep against enterotoxaemia.

F199E substitution reduced toxicity of Clostridium perfringens epsilon toxin by depriving the receptor binding capability

Epsilon toxin (ETX), a potent toxin, is produced by types B and D strains of Clostridium perfringens, which could cause severe diseases in humans and domestic animals. Mutant rETX^F199E was previously demonstrated to be a good vaccine candidate. However, the mechanism concerned remains unknown. To clarify how F199E substitution reduced ETX toxicity, we performed a series of experiments. The results showed that the cell-binding and pore-forming ability of rETX^F199E was almost abolished. We speculated that F199E substitution reduced toxicity by depriving the receptor binding capability of ETX, which contributed to the hypothesis that domain I of ETX is responsible for cell binding. In addition, our data suggested that ETX could cause Ca²⁺ release from intracellular Ca²⁺ stores, which may underlie an alternate pathway leading to cell death. Furthermore, ETX induced crenation of the MDCK cells was observed, with sags and crests first appearing on the surface of condensed MDCK cells, according to scanning electron microscopy. The data also demonstrated the safety and potentiality of rETX^F199E as a vaccine candidate for humans. In summary, findings of this work potentially contribute to a better understanding of the pathogenic mechanism of ETX and the development of vaccine against diseases caused by ETX, using mutant proteins.

Mapping of the continuous epitopes displayed on the Clostridium perfringens type D epsilon-toxin

The epsilon toxin, produced by Clostridium perfringens, is responsible for enterotoxemia in ruminants and is a potential bioterrorism agent. In the present study, 15 regions of the toxin were recognized by antibodies present in the serum, with different immunodominance scales, and may be antigen determinants that can be used to formulate subunit vaccines.

The Use of Next-Generation Sequencing in the Identification of a Fastidious Pathogen: A Lesson From a Clinical Setup

Clostridium haemolyticum is the causal agent of bacillary hemoglobinuria in cattle, goat, sheep, and ruminants. In this study, we report the first recorded human-infecting C. haemolyticum strain collected from an 18-year-old woman diagnosed with acute lymphoblastic leukemia. After failure of traditional techniques, only next-generation sequencing (NGS) technology in combination with bioinformatics, phylogenetic, and pathogenomics analyses revealed that our King Faisal Specialist Hospital and Research Center (KFSHRC) bacterial isolate belongs to C. haemolyticum species. KFSHRC isolate is composed of 1 chromosome and 4 plasmids. The total genome size is estimated to be 2.7 Mbp with a low GC content of 28.02%. Comparative pathogenomics analysis showed that C. haemolyticum KFSHRC isolate is a potential virulent pathogenic bacterium as it possesses the virulence factors necessary to establish an infection, acquire essential nutrients, resist antimicrobial agents, and tolerate hostile conditions both in the human host and in its surrounding environment. These factors are included in the main chromosome in addition to novel recombination of the plasmids, and they could be the reason for the incidence of that human infection. This work demonstrated the importance of using NGS in medical microbiology for pathogen identification. It also demonstrates the importance of sequencing more microbial samples and sharing this information in public databases to facilitate the identification of pathogenic microbes with better accuracy.

Complete Sequence and Organization of pFR260, the INTA Fr7-4 Plasmid Harboring Insecticidal Genes

We report the complete sequence and analysis of pFR260, a novel megaplasmid of 260,595 bp from the <i>Bacillus thuringiensis</i> strain INTA Fr7-4 isolated in Argentina. It carries 7 insecticidal genes: 3 <i>cry8</i> copies previously reported, 2 <i>vip1,</i> and 2 <i>vip2</i>. Also, it carries a gene encoding a putative atypical Cry protein. These genes are arranged in a region of approximately 105 kbp in size with characteristics of a pathogenicity island with a potential coleopteran-specific insecticide profile. DNA strand composition asymmetry, as determined by GC skew analysis, and the presence of a Rep protein involved in the initiation of replication suggest a bidirectional <i>theta</i> mechanism of replication. In addition, many genes involved in conjugation and a CRISPR-Cas system were detected. The pFR260 sequence was deposited in GenBank under accession number KX258624.

Structural pierce into molecular mechanism underlying Clostridium perfringens Epsilon toxin function

Epsilon toxin of the Clostridium perfringens garnered a lot of attention due to its potential for toxicity in humans, extreme potency for cytotoxicity in mice and lack of any approved therapeutics prescribed for human. However, the intricacies of the Epsilon toxin action mechanism are yet to be understood. In this regard, various in silico tools have been exploited to model and refine the 3D structure of the toxin and its two receptors. The receptor proteins were embedded into designed lipid membranes within an aqueous and ionized environment. Thereafter, the modeled structures subjected to series of consecutive molecular dynamics runs to achieve the most natural like coordination for each model. Ultimately, protein-protein interaction analyses were performed to understand the probable action mechanism. The obtained results successfully confirmed the accuracy of employed methods to achieve high quality models for the toxin and its receptors within their lipid bilayers. Molecular dynamics analyses lead the structures to a more native like coordination. Moreover, the results of previous empirical studies were confirmed, while new insights for action mechanisms including the detailed roles of Hepatitis A virus cellular receptor 1 (HAVCR1) and Myelin and lymphocyte protein (MAL) proteins were achieved. In light of previous and our observations, we suggested novel models which elucidated the existing interplay between potential players of Epsilon toxin action mechanism with detailed structural evidences. These models would pave the way to have more robust understanding of the Epsilon toxin biology, more precise vaccine construction and more successful drug (inhibitor) design.