Membrane-Binding Mechanism of Clostridium perfringens Alpha-Toxin

Unveiling the pathogenic mechanisms of Clostridium perfringens toxins and virulence factors

Clostridium perfringens causes multiple diseases in humans and animals. Its pathogenic effect is supported by a broad and heterogeneous arsenal of toxins and other virulence factors associated with a specific host tropism. Molecular approaches have indicated that most C. perfringens toxins produce membrane pores, leading to osmotic cell disruption and apoptosis. However, identifying mechanisms involved in cell tropism and selective toxicity effects should be studied more. The differential presence and polymorphisms of toxin-encoding genes and genes encoding other virulence factors suggest that molecular mechanisms might exist associated with host preference, receptor binding, and impact on the host; however, this information has not been reviewed in detail. Therefore, this review aims to clarify the current state of knowledge on the structural features and mechanisms of action of the major toxins and virulence factors of C. perfringens and discuss the impact of genetic diversity of toxinotypes in tropism for several hosts.

Genomic analysis of Clostridium perfringens type D isolates from goat farms

C. perfringens type D strains are the leading cause of enterotoxaemia in ruminants such as goats, sheep, and cattle. However, there has been no prior research on the genomic characteristics of C. perfringens type D strains from various regions in China. Here, we investigated the antibiotic resistance, genomic characteristics, and phylogenetic relationship of C. perfringens type D isolates recovered from goat farms in Shaanxi, Gansu, and Ningxia provinces. The antibiotic resistance test indicated that the isolates displayed high minimum inhibitory concentration (MIC) values to sulfafurazole, whereas the other antibiotics tested, such as penicillin, enrofloxacin, and florfenicol, worked well on them. Additionally, only tetracycline resistance genes [tetA(P) and tetB(P)] were identified from the isolates. A collective of 13 toxin genes, including etx and cpe were detected among the isolates. Sequence comparison revealed that the etx and cpe genes shared high sequence identities, and they could coexist on a pCW3-like plasmid, representing a potential risk to both animal breeding and public health. Phylogenetic analysis using core genome multi-locus sequence typing (cgMLST) and core genome single nucleotide polymorphisms (SNPs) revealed the close genetic relationship and potential regional/transregional transmission of the C. perfringens type D isolates in Shaanxi and Gansu provinces. Furthermore, pan-genomic analysis suggested the functional differences at the protein-coding gene level, although isolates from the same source shared a close genetic relationship. In conclusion, this study indicated the antibiotic resistance, virulence markers, potential transregional transmission, and genomic diversity of C. perfringens type D strains from various regions in China, which could provide references for the prevention of C. perfringens foodborne diseases and further research.

Mechanisms of intestinal epithelial cell damage by Clostridiumperfringens

Clostridium perfringens, a Gram-positive bacterium, causes intestinal diseases in humans and livestock through its toxins, related to alpha toxin (CPA), beta toxin (CPB), C. perfringens enterotoxin (CPE), epsilon toxin (ETX), Iota toxin (ITX), and necrotic enteritis B-like toxin (NetB). These toxins disrupt intestinal barrier, leading to various cell death mechanisms such as necrosis, apoptosis, and necroptosis. Additionally, non-toxin factors like adhesins and degradative enzymes contribute to virulence by enhancing colonization and survival of C. perfringens. A vicious cycle of intestinal barrier breach, misregulated cell death, and subsequent inflammation is at the heart of chronic inflammatory and infectious gastrointestinal diseases. Understanding these mechanisms is essential for developing targeted therapies against C. perfringens-associated intestinal diseases.

Purinergic Receptor Antagonists Inhibit Hemolysis Induced by Clostridium perfringens Alpha Toxin

Clostridium perfringens alpha toxin (CPA), which causes yellow lamb disease in sheep and gas gangrene and food poisoning in humans, is produced by all types of C. perfringens and is the major virulence determinant of C. perfringens type A. CPA induces hemolysis in many species, including humans, murines, sheep and rabbits, through its enzymatic activity, which dissolves the cell membrane. Recent studies have shown that some pore-forming toxins cause hemolysis, which is achieved by the activation of purinergic receptors (P2). However, the relationship between P2 receptors and non-pore-forming toxin hemolysis has not been investigated. In the present study, we examined the function of P2 receptors in CPA toxin hemolysis and found that CPA-induced hemolysis was dependent on P2 receptor activation, and this was also true for Staphylococcus aureus β-Hemolysin, another non-pore-forming toxin. Furthermore, we use selective P2 receptor antagonists to demonstrate that P2X1 and P2X7 play important roles in the hemolysis of human and murine erythrocytes. In addition, we found that redox metabolism was mainly involved in CPA-induced hemolysis using metabolomic analysis. We further demonstrate that CPA activates P2 receptors and then activates NADPH oxidase through the PI3K/Akt and MEK1/ERK1 pathways, followed by the production of active oxygen to induce hemolysis. These findings contribute to our understanding of the pathological effects of CPA, clarify the relationship between P2 activation and non-pore-forming toxin-induced hemolysis, and provide new insights into CPA-induced hemolysis.

The Effects of Bacillus amyloliquefaciens SC06 on Behavior and Brain Function in Broilers Infected by Clostridium perfringens

Poultry studies conducted on Clostridium perfringens (CP) mainly focus on the effects of intestinal health and productive performance. Notably, the probiotic Bacillus amyloliquefaciens SC06 (BaSC06) is known to play a role in preventing bacterial infection. However, whether CP could induce the changes in brain function and behaviors and whether BaSC06 could play roles in these parameters is yet to be reported. The aim of this study was to evaluate the effects of BaSC06 on stress-related behaviors and gene expression, as well as the brain morphology and mRNA sequence of the hypothalamus in broiler chickens. A total of 288 one-day-old chicks were randomly divided into four groups: (1) a control group with no treatment administered or infection; (2) birds treated with the BaSC06 group; (3) a CP group; and (4) a BaSC06 plus CP (Ba_CP) group. The results showed that stress and fear-related behaviors were significantly induced by a CP infection and decreased due to the treatment of BaSC06. CP infection caused pathological damage to the pia and cortex of the brain, while BaSC06 showed a protective effect. CP significantly inhibited hypothalamic GABA and promoted HTR1A gene expression, while BaSC06 promoted GABA and decreased HTR1A gene expression. The different genes were nearly found between the comparisons of control vs. Ba group and Ba vs. CP group, while there were a great number of different genes between the comparisons of control vs. Ba_CP as well as CP vs. Ba_CP. Several different gene expression pathways were found that were related to disease, energy metabolism, and nervous system development. Our results will help to promote poultry welfare and health, as well as provide insights into probiotics to replace antibiotics and reduce resistance in the chicken industry.

Cooperation of quorum sensing and central carbon metabolism in the pathogenesis of Gram-positive bacteria

Quorum sensing (QS), an integral component of bacterial communication, is essential in coordinating the collective response of diverse bacterial pathogens. Central carbon metabolism (CCM), serving as the primary metabolic hub for substances such as sugars, lipids, and amino acids, plays a crucial role in the life cycle of bacteria. Pathogenic bacteria often utilize CCM to regulate population metabolism and enhance the synthesis of specific cellular structures, thereby facilitating in adaptation to the host microecological environment and expediting infection. Research has demonstrated that QS can both directly or indirectly affect the CCM of numerous pathogenic bacteria, thus altering their virulence and pathogenicity. This article reviews the interplay between QS and CCM in Gram-positive pathogenic bacteria, details the molecular mechanisms by which QS modulates CCM, and lays the groundwork for investigating bacterial pathogenicity and developing innovative infection treatment drugs.

Exploring the Genomic Landscape of Bacillus paranthracis PUMB_17 as a Proficient Phosphatidylcholine-Specific Phospholipase C Producer

Phospholipases find versatile applications across industries, including detergent production, food modification, pharmaceuticals (especially in drug delivery systems), and cell signaling research. In this study, we present a strain of Bacillus paranthracis for the first time, demonstrating significant potential in the production of phosphatidylcholine-specific phospholipase C (PC-PLC). The investigation thoroughly examines the B. paranthracis PUMB_17 strain, focusing on the activity of PC-PLC and its purification process. Notably, the PUMB_17 strain displays extracellular PC-PLC production with high specific activity during the late exponential growth phase. To unravel the genetic makeup of PUMB_17, we employed nanopore-based whole-genome sequencing and subsequently conducted a detailed genome annotation. The genome comprises a solitary circular chromosome spanning 5,250,970 bp, featuring a guanine-cytosine ratio of 35.49. Additionally, two plasmids of sizes 64,250 bp and 5845 bp were identified. The annotation analysis reveals the presence of 5328 genes, encompassing 5186 protein-coding sequences, and 142 RNA genes, including 39 rRNAs, 103 tRNAs, and 5 ncRNAs. The aim of this study was to make a comprehensive genomic exploration that promises to enhance our understanding of the previously understudied and recently documented capabilities of Bacillus paranthracis and to shed light on a potential use of the strain in the industrial production of PC-PLC.

Exploring the predictive power of jejunal microbiome composition in clinical and subclinical necrotic enteritis caused by Clostridium perfringens: insights from a broiler chicken model

BACKGROUND

Necrotic enteritis (NE) is a severe intestinal infection that affects both humans and poultry. It is caused by the bacterium Clostridium perfringens (CP), but the precise mechanisms underlying the disease pathogenesis remain elusive. This study aims to develop an NE broiler chicken model, explore the impact of the microbiome on NE pathogenesis, and study the virulence of CP isolates with different toxin gene combinations.

METHODS

This study established an animal disease model for NE in broiler chickens. The methodology encompassed inducing abrupt protein changes and immunosuppression in the first experiment, and in the second, challenging chickens with CP isolates containing various toxin genes. NE was evaluated through gross and histopathological scoring of the jejunum. Subsequently, jejunal contents were collected from these birds for microbiome analysis via 16S rRNA amplicon sequencing, followed by sequence analysis to investigate microbial diversity and abundance, employing different bioinformatic approaches.

RESULTS

Our findings reveal that CP infection, combined with an abrupt increase in dietary protein concentration and/or infection with the immunosuppressive variant infectious bursal disease virus (vIBDV), predisposed birds to NE development. We observed a significant decrease (p < 0.0001) in the abundance of Lactobacillus and Romboutsia genera in the jejunum, accompanied by a notable increase (p < 0.0001) in Clostridium and Escherichia. Jejunal microbial dysbiosis and severe NE lesions were particularly evident in birds infected with CP isolates containing cpa, netB, tpeL, and cpb2 toxin genes, compared to CP isolates with other toxin gene combinations. Notably, birds that did not develop clinical or subclinical NE following CP infection exhibited a significantly higher (p < 0.0001) level of Romboutsia. These findings shed light on the complex interplay between CP infection, the gut microbiome, and NE pathogenesis in broiler chickens.

CONCLUSION

Our study establishes that dysbiosis within the jejunal microbiome serves as a reliable biomarker for detecting subclinical and clinical NE in broiler chicken models. Additionally, we identify the potential of the genera Romboutsia and Lactobacillus as promising candidates for probiotic development, offering effective alternatives to antibiotics in NE prevention and control.

Moringa oleifera as a potential antimicrobial against pathogenic Clostridium perfringens isolates in farm animals

Background

Clostridium perfringens (CP) is an emerging anaerobic pathogen that can aggravate severe fatal infections in different hosts and livestock.

Aim

This paper was designed to monitor the antibacterial efficacy of Moringa oleifera (M. oleifera) plant against different CP isolates of variant toxin genotypes comparing that with commercial antibiotics in the veterinary field.

Methods

A total of 200 examined fecal, intestinal, and liver samples from cattle, sheep, and goats were investigated bacteriologically and biochemically for CP. Then, the isolates were examined by polymerase chain reaction (PCR) for toxin gene typing. Thereafter, the antimicrobial susceptibility testing as well as the antibacterial efficacy of M. oleifera were evaluated and statistically analyzed against recovered isolates.

Results

The prevalence rate of CP was 51% (102/200); of which 54.5% was from cattle, 50% from sheep, and 40% from goat. Moreover, all CP isolates were highly resistant to tetracycline and lincomycin drugs; meanwhile, they were of the least resistance against ciprofloxacin (8.3%-16.7%), cefotaxime (16.7%-25%), and gentamycin (26.7%-33.3%). For M. oleifera, high antibacterial efficacy with greater inhibition zones of the plant was recorded with its oil (20-24 mm) and ethanolic extracts (16-20 mm) against CP than the aqueous extract (≤ 10 mm). A good correlation was stated between M. oleifera oil and toxin type of CP isolates particularly type A followed by D and B types. Interestingly, the oil and ethanolic extracts of M. oleifera gave higher antibacterial efficacy than most commercial antibiotics against the recovered isolates.

Conclusion

This study highlighted the potent antibacterial properties of M. oleifera for suppressing CP isolated from farm animals; hence, more investigations on M. oleifera are suggested to support its use as a medical herbal plant substituting antibiotics hazards and resistance problems worldwide.

Immunization of sheep with a recombinant vaccine containing immunogenic nontoxic domains of Clostridium perfringens alpha and beta toxins

Clostridium perfringens (types A and C) can cause several diseases by secreting alpha (CPA) and beta (CPB) exotoxins in the gastrointestinal tract. Although vaccination is the main measure of immunization against C. perfringens, available vaccines have limitations in terms of productivity and safety. Thus, recombinant vaccines are an important, more effective, practical, and safer strategy in the immunization of animals. In this study, we evaluated the immunization of sheep with recombinant Escherichia coli bacterins expressing CPA and CPB complete proteins (co-administered), the immunogenic nontoxic domains rCPA-C247-370 and rCPB-C143-311 co-administered or fused as a bivalent chimera (rCPBcAc). For this, in silico analysis was performed to design rCPBcAc, considering the stability of the mRNA (-278.80 kcal/mol), the degree of antigenicity (0.7557), the epitopes of the B cell ligand, and different physicochemical characteristics. All proteins were expressed in vitro. In vivo, animals vaccinated with the co-administered antigens rCPA + rCPB and rCPA-C+ rCPB-C (200 μg each) had mean CPA and CPB neutralizing antitoxin titers of 4, 10, 4.8, and 14.4 IU/mL, respectively, while those vaccinated with 200 μg of rCPBcAc chimera (approximately 100 μg of each antigen) had titers of <4 and 12 IU/mL of CPA and CPB antitoxins, respectively, 56 days after the administration of the first dose. In addition, the chimera was considered to be immunogenic for inducing antitoxin titers using the half dose. In this study, we presented a new recombinant antigen potentially applicable for vaccines against the CPA and CPB toxins for preventing diseases caused by Clostridium perfringens.

Antimicrobial potential of myricetin-coated zinc oxide nanocomposite against drug-resistant Clostridium perfringens

BACKGROUND

Clostridium perfringens (C. perfringens) is an important pathogen in livestock animals and humans causing a wide array of systemic and enteric diseases. The current study was performed to investigate the inhibitory activity of myricetin (MYR), polyvinyl alcohol (PVA), and zinc oxide (ZnO) nanocomposite against growth and α-hemolysin of C. perfringens isolated from beef meat and chicken sources.

RESULTS

The overall occurrence of C. perfringens was 29.8%. The prevalence of C. perfringens was higher in chicken (38.3%) than in beef meat products (10%). The antimicrobial susceptibility testing revealed that C. perfringens isolates exhibited high resistance levels for metronidazole (93%), bacitracin (89%), penicillin G (84%), and lincomycin (76%). Of note, 1% of C. perfringens isolates were pandrug-resistant (PDR), 4% were extensive drug-resistant (XDR), while 91% were multidrug-resistant. The results of broth microdilution technique revealed that all tested C. perfringens isolates were susceptible to MYR-loaded ZnO/PVA with minimum inhibitory concentrations (MICs) ranged from 0.125 to 2 µg/mL. Moreover, the MYR either alone or combined with the nanocomposite had no cytotoxic activities on chicken red blood cells (cRBCs). Transcriptional modifications of MYR, ZnO, ZnO/PVA, and ZnO/PVA/MYR nanocomposite were determined, and the results showed significant down-regulation of α-hemolysin fold change to 0.5, 0.7, 0.6, and 0.28, respectively compared to the untreated bacteria.

CONCLUSION

This is an in vitro study reporting the antimicrobial potential of MYR-coated ZnO nanocomposite as an effective therapeutic candidate against C. perfringens. An in vivo approach is the next step to provide evidence for applying these alternatives in the treatment and prevention of C. perfringens-associated diseases.

Metabonomic Analysis of Metabolites Produced by Escherichia coli in Patients With and Without Sepsis

AIM

To analyze the metabolites of the most common sepsis-related pathogen and their correlation with clinical indicators.

METHODS

Information of bacterial-infection patients in Huzhou Central hospital was retrospectively investigated and analyzed. The most common pathogen inducing sepsis was selected. Then, the metabolic profiles of pathogens from blood were detected by liquid chromatography/mass spectrometry. Cluster and classification analysis, KEGG pathway enrichment analysis, multidimensional OPLS-DA, Z scores, correlation analysis were used to analyze the metabolites.

RESULTS

Escherichia coli (E. coli) was the pathogen that caused the most infection (about 21%) and sepsis. Amino acids, peptides, terpene glycosides, carbohydrates were the main metabolites of E.coli and they were mainly digestive and endocrine-related compounds. Most of them were related to amino acids metabolism, cofactors and vitamins metabolism, biosynthesis of secondary metabolites, et al. Moreover, metabolites were involved in purine metabolism, neuroactive ligand-receptor interaction, ABC transporters, etc. Then, over 70 differential metabolites such as tyramine, tryptophan, 3- hydroxymalondialdehyde were screened in E.coli from nonseptic and septic patients. They were mainly involved in phenylalanine metabolism, tryptophan metabolism, protein digestion and absorption. Distribution of metabolites of E. coli from nonseptic and septic patients was obviously different. What is more, differential metabolites had evidently correlation with SOFA score, APPACHE II score, C-reactive protein, erythrocyte, platelet, aspartate aminotransferase, coagulation function, lactic acid (p < 0.01).

CONCLUSION

The different metabolic profile of E. coli from nonseptic and septic patients indicated that differential metabolites might be associated with sepsis.

Necrotic Enteritis in Broiler Chickens: A Review on the Pathogen, Pathogenesis, and Prevention

Clostridium perfringens type A and C are the primary etiological agents associated with necrotic enteritis (NE) in poultry. The predisposing factors implicated in the incidence of NE changes the physical properties of the gut, immunological status of birds, and disrupt the gut microbial homeostasis, causing an over-proliferation of C. perfringens. The principal virulence factors contributing to the pathogenesis of NE are the α-toxin, β-toxin, and NetB toxin. The immune response to NE in poultry is mediated by the Th1 pathway or cytotoxic T-lymphocytes. C. perfringens type A and C are also pathogenic in humans, and hence are of public health significance. C. perfringens intoxications are the third most common bacterial foodborne disease after Salmonella and Campylobacter. The restrictions on the use of antibiotics led to an increased incidence of NE in poultry. Hence, it is essential to develop alternative strategies to keep the prevalence of NE under check. The control strategies rely principally on the positive modulation of host immune response, nutritional manipulation, and pathogen reduction. Current knowledge on the etiology, pathogenesis, predisposing factors, immune response, effect on the gut microbial homeostasis, and preventative strategies of NE in this post-antibiotic era is addressed in this review.

Yellow Lamb Disease (Clostridium perfringens Type A Enterotoxemia of Sheep): A Review

Simple Summary

Yellow lamb disease is a poorly researched and understood condition that seems to affect young sheep. The disease is characterized by hemolysis and is thought to be caused by alpha toxin-producing Clostridium perfringens type A, although a definitive association with this microorganism has not been confirmed. This is due, in part, to the ubiquitous nature of C. perfringens type A, which is naturally present in the intestine of healthy sheep, a fact that complicates the diagnosis. In this review, we summarize the available information on the etiology, clinical signs, lesions, diagnosis, prevention and prophylaxis of yellow lamb disease.

Abstract

Yellow lamb disease is an infrequent disease in sheep for which there is scant literature, and that has been reported in the US, Australia, New Zealand, South Africa and Europe, although anecdotal evidence indicates that it may have also been diagnosed in South America. The disease is produced by some strains of Clostridium perfringens type A that produce unusually high levels of alpha- toxin. Because C. perfringens type A is ubiquitous and is found in the intestine of most clinically healthy sheep, diagnosis of yellow lamb disease is challenging and requires quantitating the amount of this microorganism present in feces and/or intestinal content. Clinically, yellow lamb disease is characterized by depression, anemia, icterus and hemoglobinuria. Occasionally, sudden death may occur. Gross findings include generalized icterus, red urine in the bladder, enlarged, pale, and friable spleen, enlarged liver with an acinar pattern, and dark, swollen kidneys. Microscopically, yellow lamb disease is characterized by centrilobular necrosis of the liver, hemoglobinuria-associated acute tubular injury, splenic congestion, pulmonary congestion and edema. Although there are no vaccines specifically designed to prevent yellow lamb disease, several vaccines against the different types of C. perfringens may afford at least some level of protection against yellow lamb disease.

Clostridium perfringens-Induced Necrotic Diseases: An Overview

Clostridium perfringens, a prevalent Gram-positive bacterium, causes necrotic diseases associated with abundant life loss and economic burdens of billions of USD. The mechanism of C. perfringens-induced necrotic diseases remains largely unknown, in part, because of the lack of effective animal models and the presence of a large array of exotoxins and diverse disease manifestations from the skin and deep tissues to the gastrointestinal tract. In the light of the advancement of medical and veterinary research, a large body of knowledge is accumulating on the factors influencing C. perfringens-induced necrotic disease onset, development, and outcomes. Here, we present an overview of the key virulence factors of C. perfringens exotoxins. Subsequently, we focus on comprehensively reviewing C. perfringens-induced necrotic diseases such as myonecrosis, acute watery diarrhea, enteritis necroticans, preterm infant necrotizing enterocolitis, and chicken necrotic enteritis. We then review the current understanding on the mechanisms of myonecrosis and enteritis in relation to the immune system and intestinal microbiome. Based on these discussions, we then review current preventions and treatments of the necrotic diseases and propose potential new intervention options. The purpose of this review is to provide an updated and comprehensive knowledge on the role of the host–microbe interaction to develop new interventions against C. perfringens-induced necrotic diseases.

Clostridium perfringens sepsis after pancreatoduodenectomy: a case report

Background

Clostridium perfringens sepsis associated with massive intravascular hemolysis has an extremely poor prognosis. We here report a case of C. perfringens sepsis associated with massive intravascular hemolysis that developed secondary to a post-pancreaticoduodenectomy (PD) hepatic abscess.

Case presentation

A 70-year-old man with Type 2 diabetes underwent PD for an ampulla of Vater carcinoma. His postoperative course was uneventful. He was discharged on the 16th post-operative day (POD 16) after confirming no major abnormalities on abdominal contrast computed tomography (CT) on POD 14 or laboratory results on POD 16. Two days after discharge, he was readmitted because of fever and chills. Laboratory tests showed only a mild inflammatory reaction (white blood cell count, 11,980/mm³; C-reactive protein, 2.07 mg/dL). Abdominal CT showed an irregular, approximately 20-mm diameter, low-density area in the liver S6 region that had not been seen on a recent previous scan. We initially suspected postoperative cholangitis associated with biliary reconstruction and started empirical treatment with sulbactam/ampicillin after drawing blood for culture. Eight hours after admission, he developed septic shock with body temperature 40.0 ℃ and blood pressure 70/40 mm Hg. Laboratory findings showed a severe inflammatory reaction, severe anemia, and massive hemolysis (white blood cell count, 37,400/mm³; hemoglobin, 7.7 g/dL; total bilirubin, 8.05 mg/dL; direct bilirubin, 2.66 mg/dL; and lactate dehydrogenase, 1686 U/L). Hemoglobinuria was noted in the urinary catheter output. Repeat CT 9 h after admission showed the low-density area in S6 had become a gas-forming abscess. C. perfringens sepsis was strongly suspected on the basis of these findings and the abscess was drained percutaneously immediately after its diagnosis. His vital signs improved dramatically and he recovered within 24 h. Blood and abscess cultures grew C. perfringens 4 days after admission, leading to a definitive diagnosis of C. perfringens sepsis associated with massive intravascular hemolysis. He was discharged 18 days after admission. His sepsis has not recurred.

Conclusions

Clostridium perfringens infection should be considered in patients who have undergone PD and present with gas-forming hepatic abscesses and/or sepsis associated with intravascular hemolysis. Prompt aggressive treatment is crucial, because C. perfringens infections can cause death within hours.

Role of Clostridium perfringens Necrotic Enteritis B-like Toxin in Disease Pathogenesis

Necrotic enteritis (NE) is a devastating enteric disease caused by Clostridium perfringens type A/G that impacts the global poultry industry by compromising the performance, health, and welfare of chickens. Coccidiosis is a major contributing factor to NE. Although NE pathogenesis was believed to be facilitated by α-toxin, a chromosome-encoded phospholipase C enzyme, recent studies have indicated that NE B-like (NetB) toxin, a plasmid-encoded pore-forming heptameric protein, is the primary virulence factor. Since the discovery of NetB toxin, the occurrence of NetB⁺ C. perfringens strains has been increasingly reported in NE-afflicted poultry flocks globally. It is generally accepted that NetB toxin is the primary virulent factor in NE pathogenesis although scientific evidence is emerging that suggests other toxins contribute to NE. Because of the complex nature of the host-pathogen interaction in NE pathogenesis, the interaction of NetB with other potential virulent factors of C. perfringens needs better characterization. This short review will summarize the primary virulence factors involved in NE pathogenesis with an emphasis on NetB toxin, and a new detection method for large-scale field screening of NetB toxin in biological samples from NE-afflicted commercial broiler flocks.

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.

Navarro M, Li J, Shrestha A, Uzal F, A. McClane B. Pathogenicity and virulence of Clostridium perfringens

Clostridium perfringens is an extremely versatile pathogen of humans and livestock, causing wound infections like gas gangrene (clostridial myonecrosis), enteritis/enterocolitis (including one of the most common human food-borne illnesses), and enterotoxemia (where toxins produced in the intestine are absorbed and damage distant organs such as the brain). The virulence of this Gram-positive, spore-forming, anaerobe is largely attributable to its copious toxin production; the diverse actions and roles in infection of these toxins are now becoming established. Most C. perfringens toxin genes are encoded on conjugative plasmids, including the pCW3-like and the recently discovered pCP13-like plasmid families. Production of C. perfringens toxins is highly regulated via processes involving two-component regulatory systems, quorum sensing and/or sporulation-related alternative sigma factors. Non-toxin factors, such as degradative enzymes like sialidases, are also now being implicated in the pathogenicity of this bacterium. These factors can promote toxin action in vitro and, perhaps in vivo, and also enhance C. perfringens intestinal colonization, e.g. NanI sialidase increases C. perfringens adherence to intestinal tissue and generates nutrients for its growth, at least in vitro. The possible virulence contributions of many other factors, such as adhesins, the capsule and biofilms, largely await future study.

Clonal diversity of Clostridium perfringens human clinical isolates with various toxin gene profiles based on multilocus sequence typing and alpha-toxin (PLC) typing

OBJECTIVES

Clostridium perfringens is a common anaerobic pathogen causing enteritis/enterocolitis and wound infections in humans. We analyzed clonal diversity and toxin gene prevalence in C. perfringens clinical isolates from humans in northern Japan.

METHODS

Prevalence of nine toxin genes was analyzed for 585 C. perfringens isolates from patients collected for 20-month period between May 2019 and December 2020 by molecular methods. Sequence type (ST) based on multilocus sequence typing (Xiao's scheme) and alpha-toxin (PLC) sequence type were determined for a total of 124 isolates selected in the present study along with those in our previous study (2017-2018).

RESULTS

Toxinotypes A (68.2%) was the most frequent, followed by F (31.6%), and G (0.2%), while additional toxin genes encoding binary enterotoxin (BEC/CPILE) and beta2 toxin were identified in one and six isolates, respectively. Among the 124 isolates with various toxin gene profiles, 62 STs including 53 novel types were identified, revealing the presence of six clonal complexes (CCs) consisting of 27 STs. Most of enterotoxin gene (cpe)-positive isolates belonged to CC36, CC41, and CC117. Based on 22 key amino acids in alpha toxin sequence, four PLC types (I-IV) including 21 subtypes were classified, and their relation to individual STs/CCs was clarified. Two isolates harboring bec/cpile belonged to different STs (ST95, ST131) and PLC types (If, IVb), indicating distribution of this toxin gene to distinct lineages.

CONCLUSIONS

The present study revealed the diversity in C. perfringens clones of human origin with various toxin gene profiles represented by ST/CC and PLC type.

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.

Evaluation of the expression and immunogenicity of four versions of recombinant Clostridium perfringens beta toxin designed by bioinformatics tools

Beta toxins (CPB) produced by Clostridium perfringens type B and C cause various diseases in animals, and the use of toxoids is an important prophylactic measure against such diseases. Promising recombinant toxoids have been developed recently. However, both soluble and insoluble proteins expressed in Escherichia coli can interfere with the production and immunogenicity of these antigens. In this context, bioinformatics tools have been used to design new versions of the beta toxin, and levels of expression and solubility were evaluated in different strains of E. coli. The immunogenicity in sheep was assessed using the molecule with the greatest potential that was selected on analyzing these results. In silico analyzes, greater mRNA stability (-169.70 kcal/mol), solubility (-0.755), and better tertiary structure (-0.12) were shown by rCPB-C. None of the strains of E. coli expressed rFH8-CPB, but a high level of expression and solubility was shown by rCPB-C. Higher levels of total and neutralizing anti-CPB antibodies were observed in sheep inoculated with bacterins containing rCPB-C. Thus, this study suggests that due to higher productivity of rCPB-C in E. coli and immunogenicity, it is considered as the most promising molecule for the production of a recombinant vaccine against diseases caused by the beta toxin produced by C. perfringens type B and C.

A novel in situ methodology for visual detection of Clostridium perfringens in pork harnessing saltatory rolling circle amplification

Clostridium perfringens (C. perfringens), a prolific toxin-producing anaerobe is an important foodborne pathogen with a huge public health concern. Rapid and on-site detection of C. perfringens is of specific importance in developing countries. In the present study, saltatory rolling circle amplification (SRCA) assay was developed for culture-independent, rapid and visual detection of C. perfringens and evaluated in meat with pork as a model. The specificity of the SRCA assay was ascertained by using 62 C. perfringens and 18 non- C. perfringens strains. The analytical sensitivity of the developed SRCA, conventional and real-time PCR assays were 80 fg, 800 fg and 800 fg DNA per tube, respectively. The limit of detection of the SRCA assay was 80 CFU/g of pork in the absence of enrichment and 8 CFU/g after short enrichment of 6 h. The detection limits of 80 CFU/g and 8 CFU/g of pork were attained within 120 min and 8 h, respectively. Real-world or field relevancy of the developed assay was evaluated by screening 82 raw and processed pork samples. As the developed assay is simple, user-friendly, cost-effective and sophisticated-equipment free, it would be more suitable for on-site testing of C. perfringens in foods. To our information, this is the first report to apply SRCA for the detection of C. perfringens.

Development of a novel polymerase spiral reaction (PSR) assay for rapid and visual detection of Clostridium perfringens in meat

C. perfringens is a widespread foodborne pathogen and one of the major concerns in the meat industry. There is a need for a simple, rapid and equipment free detection system for C. perfringens as conventional anaerobic culture method is labour and resource intensive. Here, we applied a novel polymerase spiral reaction phenomenon to develop and evaluate an assay for effortless and visual detection of C. perfringens in meat foods employing pork as a representative model. Specificity of the assay was determined using 51 C perfringens and 20 non- C. perfringens strains. Analytical sensitivity of the developed test was 80 fg DNA per tube indicating 100 times more sensitivity than end-point PCR assay. The detection limits were 980 CFU/g and 9.8 × 10⁴ CFU/g of pork for PSR and PCR assays, respectively. The operation time of the PSR assay including DNA extraction was 120 min. The developed PSR assay was accurate and effective in comparison to culture method, in detecting C. perfringens in 38 of 74 pork samples. Therefore the specificity, sensitivity, negative predictive value, positive predictive value and accuracy rate of the developed PSR assay were 100%. The developed PSR assay is easy to perform, rapid, affordable, permitting sophisticated-equipment free amplification and naked eye interpretation. This is the initial report in which the PSR assay was optimized for the detection of C. perfringens.

Molecular Characterization of Clostridium perfringens Strains Isolated in Italy

Clostridium (C.) perfringens is the causative agent of several diseases and enteric infections in animals and humans. The pathogenicity of the bacterium is largely mediated by the production of a wide range of toxins. Individual C. perfringens strains produce only subsets of this toxin repertoire, which permits the classification in seven toxinotypes (A–G). In addition, a variety of minor toxins further characterizes the single strains. The aim of this work was to evaluate, using Polymerase Chain Reaction (PCR) assays, the diversity of 632 C. perfringens strains isolated in Italy over 15 years. The genotyped strains were analyzed to determine the presence of major and minor toxins (cpe, consensus, and atypical cpb2), their geographical origins, and the source of isolation (animal species or food). Our study shows that toxinotype A had the greatest representation (93%) and correlated mainly with consensus cpb2 in a variety of animal species, as well as with atypical cpb2 in the five food samples. Type D, associated with cpe and atypical cpb2 minor toxins, was identified in 3% of the cases, and type F was identified in 2.5%. Seven type C isolates (1.1%) were detected in cattle, whereas the only type B atypical cpb2 isolated in Italy was detected in a goat, and one type E cpe+atypical cpb2 was detected in a sheep. Type G was not detected.

Verbascoside Protects Mice From Clostridial Gas Gangrene by Inhibiting the Activity of Alpha Toxin and Perfringolysin O

Gas gangrene, caused mainly by the anaerobic bacterium Clostridium perfringens (C. perfringens), causes death within 48 h of onset. Limited therapeutic strategies are available, and it is associated with extremely high mortality. Both C. perfringens alpha toxin (CPA) and perfringolysin O (PFO) are important virulence factors in the development of gas gangrene, suggesting that they are therapeutic targets. Here, we found that verbascoside, a phenylpropanoid glycoside widely distributed in Chinese herbal medicines, could effectively inhibit the biological activity of both CPA and PFO in hemolytic assays. The oligomerization of PFO was remarkably inhibited by verbascoside. Although no antibacterial activity was observed, verbascoside treatment protected Caco-2 cells from the damage caused by CPA and PFO. Additionally, infected mice treated with verbascoside showed significantly alleviated damage, reduced bacterial burden, and decreased mortality. In summary, verbascoside has an effective therapeutic effect against C. perfringens virulence both in vitro and in vivo by simultaneously targeting CPA and PFO. Our results provide a promising strategy and a potential lead compound for C. perfringens infections, especially gas gangrene.

Botulinum Toxin as a Biological Warfare Agent: Poisoning, Diagnosis and Countermeasures

Botulinum toxin is a neurotoxin produced by Clostridium botulinum and some other relative species. It causes a lethal disease called botulism. It can enter the body via infections by Clostridium (e.g. wound and children botulism) or by direct contact with the toxin or eating contaminated food (food-borne botulism). Botulinum toxin is also considered as a relevant biological warfare agent with an expected high number of causalities when misused for bioterrorist or military purposes. The current paper surveys the actual knowledge about botulinum toxin pathogenesis, the manifestation of poisoning, and current trends in diagnostics and therapeutics. Relevant and recent literature is summarized in this paper.

Gas gangrene in mammals: a review

Gas gangrene is a necrotizing infection of subcutaneous tissue and muscle that affects mainly ruminants and horses, but also other domestic and wild mammals. Clostridium chauvoei, C. septicum, C. novyi type A, C. perfringens type A, and C. sordellii are the etiologic agents of this disease, acting singly or in combination. Although a presumptive diagnosis of gas gangrene can be established based on clinical history, clinical signs, and gross and microscopic changes, identification of the clostridia involved is required for confirmatory diagnosis. Gross and microscopic lesions are, however, highly suggestive of the disease. Although the disease has a worldwide distribution and can cause significant economic losses, the literature is limited mostly to case reports. Thus, we have reviewed the current knowledge of gas gangrene in mammals.

Generation of recombinant baculovirus expressing atoxic C-terminal CPA toxin of Clostridium perfringens and production of specific antibodies

Background

Clostridium perfringens is the causative agent of several diseases and enteric infections in animals and humans. The virulence of C. perfringens is largely attributable to the production of numerous toxins; of these, the alpha toxin (CPA) plays a crucial role in histotoxic infections (gas gangrene). CPA toxin consists of two domains, i.e., the phospholipase C active site, which lies in the N-terminal domain amino acid (aa residues 1–250), and the C-terminal region (aa residues 251–370), which is responsible for the interaction of the toxin with membrane phospholipids in the presence of calcium ions. All currently produced clostridial vaccines contain toxoids derived from culture supernatants that are inactivated, mostly using formalin. The CPA is an immunogenic antigen; recently, it has been shown that mice that were immunized with the C-terminal domain of the toxin produced in E. coli were protected against C. perfringens infections and the anti-sera produced were able to inhibit the CPA activity. Monoclonal and polyclonal antibodies were produced only against full-length CPA and not against the truncated forms.

Results

In the present study, we have reported for the first time; about the generation of a recombinant baculovirus capable of producing a deleted rCPA toxin (rBacCPA250–363H6) lacking the N-terminal domain and the 28 amino acids (aa) of the putative signal sequence. The insertion of the L21 consensus sequence upstream of the translational start codon ATG, drastically increases the yield of recombinant protein in the baculovirus-based expression system. The protein was purified by Ni-NTA affinity chromatography and the lack of toxicity in vitro was confirmed in CaCo-2 cells. Polyclonal antibodies and eight hybridoma-secreting Monoclonal antibodies were generated and tested to assess specificity and reactivity. The anti-sera obtained against the fragment rBacCPA250–363H6 neutralized the phospholipase C activity of full-length PLC.

Conclusions

The L21 leader sequence enhanced the expression of atoxic C-terminal recombinant CPA protein produced in insect cells. The monoclonal and polyclonal antibodies obtained were specific and highly reactive. The availability of these biologicals could contribute to the development of diagnostic assays and/or new recombinant protein vaccines.

Focal duodenal necrosis in chickens: attempts to reproduce the disease experimentally and diagnostic considerations

Focal duodenal necrosis (FDN) is an intestinal disease of egg-layer chickens characterized by multifocal necrosis of the duodenal loop and proximal jejunum. Affected flocks usually have decreased egg weights and drops in egg production. Previous studies have associated this condition with Clostridium perfringens infection. We tried to reproduce FDN by experimental infection of egg-laying chickens using different netB-positive and netB-negative C. perfringens strains, and duodenal homogenate obtained from FDN lesions. Chickens challenged with C. perfringens and/or duodenal homogenate developed duodenitis after challenge. Gross lesions included mucosal erosions, hyperemia, mucosal hemorrhages, and watery intestinal content. Microscopic lesions included mild enterocyte degeneration and necrosis, and mild-to-moderate hemorrhage and lymphoplasmacytic and heterophilic infiltration of the lamina propria. Two netB-positive C. perfringens strains closely related to necrotic enteritis pathogenic strains, by genomic composition, were re-isolated from lesions. Necrosis of intestinal crypts was observed in chickens challenged with duodenal homogenate with or without C. perfringens coinfection. Characteristic microscopic FDN lesions with significant necrosis and loss of villus enterocytes were not reproduced.

Molecular structure and function of the carboxy-terminus of the alpha-toxin from Clostridium perfringens type A

In order to interpret the molecular structure and biological characteristics of Clostridium perfringens alpha-toxin (CPA), the CPA251-370 gene was cloned and the 120 amino acid carboxy terminal of CPA (CPA251-370) was obtained. The secondary and three-dimensional (3D) structures of CPA251-370 were predicted. The secondary structure of CPA251-370 consisted primarily of 35.48% β-sheets and 44.35% random coils. Compared with the CPA toxin consisting of 10 α-helices and eight β-sheets, the 3D structure of CPA251-370 only contained eight β-sheets. The circular dichroism (CD) spectrum detection showed that the CD spectrum of CPA251-370 changed slightly compared with the CD spectrum of CPA. Biological activity assays showed that CPA251-370 had lost the phospholipase C (PLC) activity and haemolytic activity of CPA. More importantly, the mice immunized with CPA251-370 were protected against a challenge with 1 MLD C. perfringens type A strain C57-1. This study laid a solid foundation for explaining the relationship between molecular structure and biological characteristics of CPA in the future. Our research also provides CPA251-370 as a candidate strains for genetic engineering subunit vaccines of C. perfringens type A.

Immunization of rabbits with recombinant Clostridium perfringens alpha toxins CPA-C and CTB-CPA-C in a bicistronic design expression system confers strong protection against challenge

The Clostridium perfringens alpha toxin (CPA), encoded by the plc gene, is the causative pathogen of gas gangrene, which is a lethal infection. In this study, we used an E. coli system for the efficient production of recombinant proteins and developed a bicistronic design (BCD) expression construct consisting of two copies of the C-terminal (247-370) domain of the alpha toxin (CPA-C) in the first cistron, followed by Cholera Toxin B (CTB) linked with another two copies of CPA-C in the second cistron that is controlled by a single promoter. Rabbits were immunized twice with purified proteins (rCPA-C rCTB-CPA-C) produced in the BCD expression system, with an inactivated recombinant E. coli vaccine (RE), C. perfringens formaldehyde-inactivated alpha toxoid (FA-CPA) and C. perfringensl-lysine/formaldehyde alpha toxoid (LF-CPA) vaccines. Following the second vaccination, 0.1 mL of pooled sera of the RE-vaccinated rabbits could neutralize 12× mouse LD₁₀₀ (100% lethal dose) of CPA, while that of the rCPA-C rCTB-CPA-C-vaccinated rabbits could neutralize 6× mouse LD₁₀₀ of CPA. Antibody titers against CPA were also assessed by ELISA, reaching titers as high as 1:2048000 in the RE group; this was significantly higher compared to the C. perfringens alpha toxoid vaccinated groups (FA-CPA and LF-CPA). Rabbits from all vaccinated groups were completely protected from a 2× rabbit LD₁₀₀ of CPA challenge. These results demonstrate that the recombinant proteins are able to induce a strong immune responses, indicating that they may be potentially utilized as targets for novel vaccines specifically against the C. perfringens alpha toxin.

Profiling of Egg Layer Flocks Affected with Focal Duodenal Necrosis Based on a Questionnaire Survey

Focal duodenal necrosis (FDN) is an intestinal disease of egg-laying chickens, characterized by multifocal mucosal erosions in the duodenal loop and proximal jejunum. It is currently considered by the Association of Veterinarians in Egg Production and the United States Animal Health Association as one of the top five disease concerns of the table egg industry in the United States. Previous studies have associated this condition with Clostridium species. The purpose of this study was to investigate the epidemiologic characteristics of table egg layer flocks affected with FDN. An online questionnaire was distributed to commercial layer operations in different states in the United States. Layer farms that had diagnosed FDN within the past 12 mo were surveyed. The questionnaire had 45 questions about management, nutrition, housing, and methods for disease prevention and control. Thirty-seven surveys were sent and 21 were completed, which represents a response rate of 56.7%. The survey results showed the presence of FDN in five egg-layer genetic lines or breed crosses of different ages, with most cases reported between 30-39 wk of age. The pullets were cage-reared in all affected flocks and the majority of flocks in production were housed in traditional cages. Most of the FDN-affected flocks received more than 12 different feed formulations from pre-lay to 60 wk of age. Distiller's dried grain with solubles was a common ingredient added to the feed in the majority of affected flocks, and all flocks were provided with limestone as a calcium source for egg production. Most surveys reported that coccidiosis and roundworm parasitism were not problems in affected flocks in production; however, pests such as flies and rodents were reported as problems in most affected flocks. Additionally, most affected farms never washed feeders, cages, and houses before disinfection, which may not be sufficient to prevent the persistency and transmission of the causative agent of FDN. In conclusion, several management practices that have been associated with enteric disease, including clostridial-associated enteritis, were described by the majority of FDN-affected flocks. Additional studies are needed to determine if management and health practices identified in this survey represent risk factors for FDN.

Advanced Proteomics as a Powerful Tool for Studying Toxins of Human Bacterial Pathogens

Exotoxins contribute to the infectious processes of many bacterial pathogens, mainly by causing host tissue damages. The production of exotoxins varies according to the bacterial species. Recent advances in proteomics revealed that pathogenic bacteria are capable of simultaneously producing more than a dozen exotoxins. Interestingly, these toxins may be subject to post-transcriptional modifications in response to environmental conditions. In this review, we give an outline of different bacterial exotoxins and their mechanism of action. We also report how proteomics contributed to immense progress in the study of toxinogenic potential of pathogenic bacteria over the last two decades.

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.

Study of the Structure and Biological Activity of the Amino-Terminus of the α-Toxin from Clostridium welchii Type A

To explore the biological activity of Clostridium welchii α-toxin (CPA), the Asp56 residue of CPA was mutated to glycine (CPA D56G) by site-directed mutagenesis, and the 250 amino acid amino-terminal phospholipase C (PLC)-containing domain of CPA (PLC1-250) was isolated. The secondary and three-dimensional (3D) structures of CPA D56G and PLC1-250 were predicted, and the results showed that the secondary structures of CPA D56G and PLC1-250 were composed of α-helices and random coils. The 3D structures of CPA D56G and PLC1-250 were similar to the 3D structures of CPA. The circular dichroism (CD) spectrum of CPA D56G differed from the CD spectrum of CPA, but the CD spectrum of PLC1-250 was similar to the CD spectrum of CPA. Biological activity assays showed that CPA D56G lost the PLC activity of CPA and that mice immunized with CPA D56G were protected against a challenge with 1 MLD C. welchii type A strain C57-1. In addition, PLC1-250 contained the PLC activity of CPA. This study laid a solid foundation for future studies on the relationship between the molecular structure and biological function of CPA and its molecular mechanism. Our study also provided CPA D56G as a candidate strain for engineering a CPA subunit vaccine for C. welchii type A.

Inactivated recombinant Escherichia coli as a candidate vaccine against Clostridium perfringens alpha toxin in sheep

Clostridium perfringens type A is the causative agent of gas gangrene and gastroenteric ("yellow lamb disease") disease in ruminants, with C. perfringens alpha toxin (CPA) being the main virulence factor in the pathogenesis of these illnesses. In the present study, we have developed recombinant Escherichia coli bacteria expressing rCPA and used it to vaccinate rabbits and sheep. Doses of up to 200 μg of rCPA used for inoculation, induced 13.82 IU.mL^-1 of neutralizing antitoxin in rabbits, which is three times higher than that recommended by the USDA (4 IU.mL^-1). In sheep, recombinant bacteria induced antitoxin titers of 4 IU.mL^-1, 56 days after the first dose. rCPA which was expressed, mainly, in inclusion bodies, was not found to influence the immunogenicity of the vaccine. The recombinant Escherichia coli bacterin, produced simply and safely, is capable of affording protection against diseases caused by C. perfringens CPA. The current findings represent a novel production method for CPA vaccines potentially applicable to veterinary medicine.

Prevalence and Genetic Diversity of Toxin Genes in Clinical Isolates of Clostridium perfringens: Coexistence of Alpha-Toxin Variant and Binary Enterotoxin Genes (bec/cpile)

Clostridium perfringens (C. perfringens) is responsible for food-borne gastroenteritis and other infectious diseases, and toxins produced by this bacterium play a key role in pathogenesis. Although various toxins have been described for C. perfringens isolates from humans and animals, prevalence of individual toxins among clinical isolates has not yet been well explored. In the present study, a total of 798 C. perfringens clinical isolates were investigated for prevalence of eight toxin genes and their genetic diversity by PCR, nucleotide sequencing, and phylogenetic analysis. Besides the alpha-toxin gene (plc) present in all the isolates, the most common toxin gene was cpe (enterotoxin) (34.2%), followed by cpb2 (beta2 toxin) (1.4%), netB (NetB) (0.3%), and bec/cpile (binary enterotoxin BEC/CPILE) (0.1%), while beta-, epsilon-, and iota-toxin genes were not detected. Genetic analysis of toxin genes indicated a high level of conservation of plc, cpe, and netB. In contrast, cpb2 was revealed to be considerably divergent, containing at least two lineages. Alpha-toxin among 46 isolates was classified into ten sequence types, among which common types were distinct from those reported for avian isolates. A single isolate with bec/cpile harbored a plc variant containing an insertion of 834-bp sequence, suggesting its putative origin from chickens.

Detection of Clostridium perfringens in tsunami deposits after the Great East Japan Earthquake

The Great East Japan Earthquake struck off the Tohoku and caused a tsunami in 2011. Most of the microbial characteristics of tsunami-affected soil remain unknown and no published study has shown how a tsunami affects the risk of infection by Clostridium perfringens living in soil. In 2011 and 2015, C. perfringens was assessed in deposits in soil from tsunami-damaged areas and undamaged areas of Miyagi. It was found that the number of C. perfringens was overwhelmingly greater in 2011 than in 2015 in the tsunami-damaged areas. According to real-time PCR, the prevalence C. perfringens organisms (%) was 10³ fold greater in the damaged than in the undamaged areas.

Multivalent Sialosides: A Tool to Explore the Role of Sialic Acids in Biological Processes

Sialic acids (Sias) are fascinating nine-carbon monosaccharides that are primarily found on the terminus of the oligosaccharide chains of glycoproteins and glycolipids on cell surfaces. These Sias undergo a variety of structural modifications at their hydroxy and amine positions, thereby resulting in structural diversity and, hence, coordinating a variety of biological processes. However, deciphering the structural functions of such interactions is highly challenging, because the monovalent binding of Sias is extremely weak. Over the last decade, several multivalent Sia ligands have been synthesized to modulate their binding affinity with proteins/lectins. In this Minireview, we highlight recent developments in the synthesis of multivalent Sia probes and their potential applications. We will discuss four key multivalent families, that is, polymers, dendrimers, liposomes, and nanoparticles, and will emphasize the major parameters that are essential for the specific interactions of these molecules with proteins in biological systems.

A sandwich duplex immuno PCR for rapid and sensitive identification of Clostridium perfringens alpha and enterotoxin

The prevalence and lethality associated with C. perfringens alpha (CPA) and enterotoxin (CPE) toxaemia necessitate the need for rapid and definitive detection systems to initiate management measures. In the present study, a sandwich duplex immuno-capture PCR (SD-IPCR) was developed by employing IgY antibodies against a bivalent protein r-Cpae derived from CPA and CPE for antigen capture and reporter antibodies against truncated CPA or CPE conjugated to oligomers of distinguishable size for antigen revealing and signal amplification. The avian immunoglobulin's (IgY) were devoid of reactivity with S. aureus protein A (SpA), a commensal that often co-exists with C. perfringens. The assay was specific, had a detection limit (LOD) of 1 pg/ml for both CPA and CPE in PBS and improved the LOD by 10⁴ folds compared to an analogous sandwich ELISA with same set of antibodies. In spiking studies, a ten-fold reduction in LOD was observed in case of intestinal tissue samples (10 pg/ml) however, no change in LOD was observed when SD-IPCR was applied on to faecal, serum or muscle tissue samples. Of the 136 natural samples examined, the SD-IPCR could detect CPA and CPE in 29.4% and 35.3% samples, while the sandwich ELISAs could detect the same in 25.7% and 25% samples respectively owing to the relatively lesser sensitivity. The LOD and specificity of the SD-IPCR demonstrates its applicability as an efficient and rapid platform for direct detection CPA and CPE from diverse samples matrices in clinical microbiological and meat testing laboratories.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

A dynamic loop provides dual control over the catalytic and membrane binding activity of a bacterial serine hydrolase

The bacterial acyl protein thioesterase (APT) homologue FTT258 from the gram-negative pathogen Francisella tularensis exists in equilibrium between a closed and open state. Interconversion between these two states is dependent on structural rearrangement of a dynamic loop overlapping its active site. The dynamics and structural properties of this loop provide a simple model for how the catalytic activity of FTT258 could be spatiotemporally regulated within the cell. Herein, we characterized the dual roles of this dynamic loop in controlling its catalytic and membrane binding activity. Using a comprehensive library of loop variants, we determined the relative importance of each residue in the loop to these two biological functions. For the catalytic activity, a centrally located tryptophan residue (Trp66) was essential, with the resulting alanine variant showing complete ablation of enzyme activity. Detailed analysis of Trp66 showed that its hydrophobicity in combination with spatial arrangement defined its essential role in catalysis. Substitution of other loop residues congregated along the N-terminal side of the loop also significantly impacted catalytic activity, indicating a critical role for this loop in controlling catalytic activity. For membrane binding, the centrally located hydrophobic residues played a surprising minor role in membrane binding. Instead general electrostatic interactions regulated membrane binding with positively charged residues bracketing the dynamic loop controlling membrane binding. Overall for FTT258, this dynamic loop dually controlled its biological activities through distinct residues within the loop and this regulation provides a new model for the spatiotemporal control over FTT258 and potentially homologous APT function.

Colocalization of receptors for Shiga toxins with lipid rafts in primary human renal glomerular endothelial cells and influence of D-PDMP on synthesis and distribution of glycosphingolipid receptors

Damage of human renal glomerular endothelial cells (HRGECs) of the kidney represents the linchpin in the pathogenesis of the hemolytic uremic syndrome caused by Shiga toxins of enterohemorrhagic Escherichia coli (EHEC). We performed a comprehensive structural analysis of the Stx-receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα4Galβ4Glcβ1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ3Galα4Galβ4Glcβ1Cer) and their distribution in lipid raft analog detergent-resistant membranes (DRMs) and nonDRMs prepared from primary HRGECs. Predominant receptor lipoforms were Gb3Cer and Gb4Cer with Cer (d18:1, C16:0), Cer (d18:1, C22:0) and Cer (d18:1, C24:1/C24:0). Stx-receptor GSLs co-distribute with sphingomyelin (SM) and cholesterol as well as flotillin-2 in DRMs, representing the liquid-ordered membrane phase and indicating lipid raft association. Lyso-phosphatidylcholine (lyso-PC) was identified as a nonDRM marker phospholipid of the liquid-disordered membrane phase. Exposure of primary HRGECs to the ceramide analogon d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) reduced total Gb3Cer and Gb4Cer content, roughly calculated from two biological replicates, down to half and quarter of its primordial content, respectively, but strengthened their prevalence and cholesterol preponderance in DRMs. At the same time, the distribution of PC, SM and lyso-PC to subcellular membrane fractions remained unaffected by D-PDMP treatment. Defining the GSL composition and precise microdomain structures of primary HRGECs may help to develop novel therapeutic options to combat life-threatening EHEC infections.

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.

Protein Toxins That Utilize Gangliosides as Host Receptors

Subsets of protein toxins utilize gangliosides as host receptors. Gangliosides are preferred receptors due to their extracellular localization on the eukaryotic cell and due to their essential nature in host physiology. Glycosphingolipids, including gangliosides, are mediators of signal transduction within and between eukaryotic cells. Protein toxins possess AB structure-function organization, where the A domain encodes a catalytic function for the posttranslational modification of a host macromolecule, including proteins and nucleic acids, and a B domain, which encodes host receptor recognition, including proteins and glycosphingolipids, alone or in combination. Protein toxins use similar strategies to bind glycans by pockets and loops, generally employing hydrogen bonding and aromatic stacking to stabilize interactions with sugars. In some cases, glycan binding facilitates uptake, while in other cases, cross-linking or a second receptor is necessary to stimulate entry. The affinity that protein toxins have for host glycans is necessary for tissue targeting, but not always sufficient to cause disease. In addition to affinity for binding the glycan, the lipid moiety also plays an important role in productive uptake and tissue tropism. Upon endocytosis, the protein toxin must escape to another intracellular compartment or into cytosol to modify a host substrate, modulating host signaling, often resulting in cytotoxic or apoptotic events in the cell, and a unique morbidity for the organism. The study of protein toxins that utilize gangliosides as host receptors has illuminated numerous eukaryotic cellular processes, identified the basis for developing interventions to prevent disease through vaccines and control bacterial diseases through therapies. In addition, subsets of these protein toxins have been utilized as therapeutic agents to treat numerous human inflictions.

Clostridium perfringens α-toxin impairs erythropoiesis by inhibition of erythroid differentiation

Clostridium perfringens α-toxin induces hemolysis of erythrocytes from various species, but it has not been elucidated whether the toxin affects erythropoiesis. In this study, we treated bone marrow cells (BMCs) from mice with purified α-toxin and found that TER119⁺ erythroblasts were greatly decreased by the treatment. A variant α-toxin defective in enzymatic activities, phospholipase C and sphingomyelinase, had no effect on the population of erythroblasts, demonstrating that the decrease in erythroblasts was dependent of its enzymatic activities. α-Toxin reduced the CD71⁺TER119⁺ and CD71^–TER119⁺ cell populations but not the CD71⁺TER119⁻ cell population. In addition, α-toxin decreased the number of colony-forming unit erythroid colonies but not burst-forming unit erythroid colonies, indicating that α-toxin preferentially reduced mature erythroid cells compared with immature cells. α-Toxin slightly increased annexinV⁺ cells in TER119⁺ cells. Additionally, simultaneous treatment of BMCs with α-toxin and erythropoietin greatly attenuated the reduction of TER119⁺ erythroblasts by α-toxin. Furthermore, hemin-induced differentiation of human K562 erythroleukemia cells was impaired by α-toxin, whereas the treatment exhibited no apparent cytotoxicity. These results suggested that α-toxin mainly inhibited erythroid differentiation. Together, our results provide new insights into the biological activities of α-toxin, which might be important to understand the pathogenesis of C. perfringens infection.

Gut dysbiosis following C-section instigates higher colonisation of toxigenic Clostridium perfringens in infants

Herein we investigated the intestinal carriage of α-toxigenic and enterotoxigenic Clostridium perfringens during infancy, focusing on its association with other gut microbes and mode of delivery and feeding. Faecal samples from 89 healthy term infants were collected at age 7 days, 1 month, 3 months, 6 months and 3 years. C. perfringens was quantified by qPCR; other gut bacteria were quantified by reverse-transcription-qPCR. Alpha-toxigenic C. perfringens was detected in 3.4% infants at day 7 but was present in 35-40% infants at subsequent time-points, with counts ranging from 10³-10⁷ cells/g faeces. Enterotoxigenic C. perfringens remained undetected at day 7 but was detected in 1.1, 4.5, 10.1 and 4.5% infants at 1 month, 3 months, 6 months and 3 years, respectively. Intriguingly, infants carrying α-toxigenic C. perfringens had lower levels of Bacteroides fragilis group, bifidobacteria, lactobacilli and organic acids as compared to non-carriers. Further analyses revealed that, compared to vaginally-born infants, caesarean-born infants had higher carriage of C. perfringens and lower levels of B. fragilis group, bifidobacteria, lactobacilli and faecal organic acids during first 6 months. Compared to formula-fed infants, breast-fed infants were slightly less often colonised with C. perfringens; and within caesarean-born infants, breast-fed infants had slightly lower levels of C. perfringens and higher levels of B. fragilis group, bifidobacteria, and lactobacilli than formula-fed infants. This study demonstrates the quantitative dynamics of toxigenic C. perfringens colonisation in infants during the early years of life. Caesarean-born infants acquire a somewhat perturbed microbiota, and breast-feeding might be helpful in ameliorating this dysbiosis. Higher carriage of toxigenic C. perfringens in healthy infants is intriguing and warrants further investigation of its sources and clinical significance in infants, particularly the caesarean-born who may represent a potential reservoir of this opportunistic pathogen and might be more prone to associated illnesses.

Recombinant Alpha, Beta, and Epsilon Toxins of Clostridium perfringens: Production Strategies and Applications as Veterinary Vaccines

Clostridium perfringens is a spore-forming, commensal, ubiquitous bacterium that is present in the gastrointestinal tract of healthy humans and animals. This bacterium produces up to 18 toxins. The species is classified into five toxinotypes (A-E) according to the toxins that the bacterium produces: alpha, beta, epsilon, or iota. Each of these toxinotypes is associated with myriad different, frequently fatal, illnesses that affect a range of farm animals and humans. Alpha, beta, and epsilon toxins are the main causes of disease. Vaccinations that generate neutralizing antibodies are the most common prophylactic measures that are currently in use. These vaccines consist of toxoids that are obtained from C. perfringens cultures. Recombinant vaccines offer several advantages over conventional toxoids, especially in terms of the production process. As such, they are steadily gaining ground as a promising vaccination solution. This review discusses the main strategies that are currently used to produce recombinant vaccines containing alpha, beta, and epsilon toxins of C. perfringens, as well as the potential application of these molecules as vaccines for mammalian livestock animals.