Analysis of protection afforded by a Clostridium perfringens α-toxoid against heterologous clostridial phospholipases C

Clostridium haemolyticum, a review of beta toxin and insights into the antigen design for vaccine development

Phospholipases C (PLCs) represent an important group of lethal toxins produced by pathogenic bacteria of the Clostridium genus, including the beta toxin of C. haemolyticum. Bacillary hemoglobinuria in cattle and sheep is the main disease caused by this pathogen and its incidence can be reduced by annual vaccination of herds. Currently, widely used vaccines depend on cultivating the pathogen and obtaining high concentrations of the toxin, disadvantages that can be overcome with the use of recombinant vaccines. In the development of this new generation of immunizing agents, identifying and understanding the structural and immunological aspects of the antigen are crucial steps, but despite this, the beta toxin is poorly characterized. Fortunately, the time and resources required for these investigations can be reduced using immunoinformatics. To advance the development of recombinant vaccines, in addition to a brief review of the structural and immunological aspects of beta toxin, this work provides in silico mapping of immunodominant regions to guide future vaccinology studies against C. haemolyticum. A review of alternatives to overcome the limitations of beta toxin vaccines (conventional or recombinant) is also proposed.

Oral Immunization of Chickens with Probiotic Lactobacillus crispatus Constitutively Expressing the α-β2-ε-β1 Toxoids to Induce Protective Immunity

Clostridium perfringens (C. perfringens) is a bacterium that commonly causes zoonotic disease. The pathogenicity of C. perfringens is a result of the combined action of α, β, and ε exotoxins. In this study, Lactobacillus crispatus (pPG-T7g10/L. crispatus) expressing the main toxoids of C. perfringens, α, ε, β1, and β2, with EGFP-labeling, was constructed, and the protective effect was estimated in chickens. The α-β2-ε-β1 toxoid was constitutively expressed for confirmation by laser confocal microscopy and western blotting, and its immunogenicity was analyzed by enzyme-linked immunosorbent assay (ELISA) and immunohistochemical assays. After booster immunization, the probiotic vaccine group showed significantly higher levels (p < 0.05) of specific secretory IgA (sIgA) and IgY antibodies in the serum and intestinal mucus. Furthermore, the levels of cytokines, including interferon (IFN)-γ, interleukin (lL)-2, IL-4, IL-10, IL-12, and IL-17, and the proliferation of spleen lymphocytes in chickens orally immunized with pPG-E-α-β2-ε-β1/L. crispatus increased significantly. Histopathological observations showed that the intestinal pathological changes in chickens immunized with pPG-E-α-β2ε-β1/L. crispatus were significantly alleviated. These data reveal that the probiotic vaccine could stimulate mucosal, cellular, and humoral immunity and provide an active defense against the toxins of C. perfringens, suggesting a promising candidate for oral vaccines against C. perfringens.

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

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

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.

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.

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.

The C-terminal domain of Clostridium perfringens alpha toxin as a vaccine candidate against bovine necrohemorrhagic enteritis

Bovine necrohemorrhagic enteritis is caused by Clostridium perfringens and leads to sudden death. Alpha toxin, together with perfringolysin O, has been identified as the principal toxin involved in the pathogenesis. We assessed the potential of alpha toxin as a vaccine antigen. Using an intestinal loop model in calves, we investigated the protection afforded by antisera raised against native alpha toxin or its non-toxic C-terminal fragment against C. perfringens-induced intestinal necrosis. Immunization of calves with either of the vaccine preparations induced a strong antibody response. The resulting antisera were able to neutralize the alpha toxin activity and the C. perfringens-induced endothelial cytotoxicity in vitro. The antisera raised against the native toxin had a stronger neutralizing activity than those against the C-terminal fragment. However, antibodies against alpha toxin alone were not sufficient to completely neutralize the C. perfringens-induced necrosis in the intestinal loop model. The development of a multivalent vaccine combining the C-terminal fragment of alpha toxin with other C. perfringens virulence factors might be necessary for complete protection against bovine necrohemorrhagic enteritis.

Toxin plasmids of Clostridium perfringens

In both humans and animals, Clostridium perfringens is an important cause of histotoxic infections and diseases originating in the intestines, such as enteritis and enterotoxemia. The virulence of this Gram-positive, anaerobic bacterium is heavily dependent upon its prolific toxin-producing ability. Many of the ∼16 toxins produced by C. perfringens are encoded by large plasmids that range in size from ∼45 kb to ∼140 kb. These plasmid-encoded toxins are often closely associated with mobile elements. A C. perfringens strain can carry up to three different toxin plasmids, with a single plasmid carrying up to three distinct toxin genes. Molecular Koch's postulate analyses have established the importance of several plasmid-encoded toxins when C. perfringens disease strains cause enteritis or enterotoxemias. Many toxin plasmids are closely related, suggesting a common evolutionary origin. In particular, most toxin plasmids and some antibiotic resistance plasmids of C. perfringens share an ∼35-kb region containing a Tn916-related conjugation locus named tcp (transfer of clostridial plasmids). This tcp locus can mediate highly efficient conjugative transfer of these toxin or resistance plasmids. For example, conjugative transfer of a toxin plasmid from an infecting strain to C. perfringens normal intestinal flora strains may help to amplify and prolong an infection. Therefore, the presence of toxin genes on conjugative plasmids, particularly in association with insertion sequences that may mobilize these toxin genes, likely provides C. perfringens with considerable virulence plasticity and adaptability when it causes diseases originating in the gastrointestinal tract.

A recombinant carboxy-terminal domain of alpha-toxin protects mice against Clostridium perfringens

Clostridium perfringens alpha-toxin (CP, 370 residues) is one of the main agents involved in the development of gas gangrene. In this study, the immunogenicity and protective efficacy of the C-terminal domain (CP251-370) of the toxin and phospholipase C (PLC; CB, 372 residues) of Clostridum bifermentans isolated from cases of clostridium necrosis were examined. The recombinant proteins were expressed as glutathione S-transferase (GST) fusion proteins. Antibodies that cross-reacted with alpha-toxin were produced after immunization with recombinant proteins including GST-CP251-370, GST-CP281-370, GST-CP311-370, CB1-372 and GST-CB251-372. Anti-GST-CP251-370, anti-GST-CP281-370 and anti-GST-CP311-370 sera neutralized both the PLC and hemolytic activities of alpha-toxin, whereas anti-CB1-372 and anti-GST-CB251-372 weakly neutralized these activities. Immunization with GST-CP251-370 and GST-CP281-370 provided protection against the lethal effects of the toxin and C. perfringens type A NCTC8237. Partial protection from the toxin and C. perfringens was elicited by immunization with GST-CP311-370 and CB1-372. GST-CP251-370 and GST-CP281-370 are promising candidates for vaccines for clostridial-induced gas gangrene.

Comparative proteomic analysis of extracellular proteins of Clostridium perfringens type A and type C strains

Clostridium perfringens is a medically important clostridial pathogen and an etiological agent causing several diseases in humans and animals. C. perfringens and its toxins have been listed as potential biological and toxin warfare (BTW) agents; thus, efforts to develop strategies for detection and protection are warranted. Forty-eight extracellular proteins of C. perfringens type A and type C strains have been identified here using a 2-dimensional gel electrophoresis-mass spectrometry (2-DE-MS) technique. The SagA protein, the DnaK-type molecular chaperone hsp70, endo-beta-N-acetylglucosaminidase, and hypothetical protein CPF_0656 were among the most abundant proteins secreted by C. perfringens ATCC 13124. The antigenic component of the exoproteome of this strain has also been identified. Most of the extracellular proteins were predicted to be involved in carbohydrate transport and metabolism (16%) or cell envelope biogenesis or to be outer surface protein constituents (13%). More than 50% of the proteins were predictably secreted by either classical or nonclassical pathways. LipoP and TMHMM indicated that nine proteins were extracytoplasmic but cell associated. Immunization with recombinant ornithine carbamoyltransferase (cOTC) clearly resulted in protection against a direct challenge with C. perfringens organisms. A significant rise in IgG titers in response to recombinant cOTC was observed in mice, and IgG2a titers predominated over IgG1 titers (IgG2a/IgG1 ratio, 2). The proliferation of spleen lymphocytes in cOTC-immunized animals suggested a cellular immune response. There were significant increases in the levels of gamma interferon (IFN-gamma) and interleukin 2 (IL-2), suggesting a Th1 type immune response.

Technical transformation of biodefense vaccines

Biodefense vaccines are developed against a diverse group of pathogens. Vaccines were developed for some of these pathogens a long time ago but they are facing new challenges to move beyond the old manufacturing technologies. New vaccines to be developed against other pathogens have to determine whether to follow traditional vaccination strategies or to seek new approaches. Advances in basic immunology and recombinant DNA technology have fundamentally transformed the process of formulating a vaccine concept, optimizing protective antigens, and selecting the most effective vaccine delivery approach for candidate biodefense vaccines.

Differential proteomic analysis of Clostridium perfringens ATCC13124; identification of dominant, surface and structure associated proteins

Background

Clostridium perfringens is a medically important clostridial pathogen causing diseases in man and animals. To invade, multiply and colonize tissues of the host, a pathogen must be able to evade host immune system, and obtain nutrients essential for growth. The factors involved in these complex processes are largely unknown and of crucial importance to understanding microbial pathogenesis. Many of the virulence determinants and putative vaccine candidates for bacterial pathogens are known to be surface localized.

Results

Using 2-DE mass spectrometry strategy, we identified major surface (22) and cell envelope (10) proteins from Clostridium perfringens ATCC13124 and those differentially expressed (11) in cells grown on cooked meat medium (CMM) in comparison with cells grown in reference state (tryptose-yeast extract-glucose medium). Riboflavin biosynthesis protein, ornithine carbamoyltransferase, cystathionine beta-lyase, and threonine dehydratase were the predominant proteins that exhibited 2.19 to 8.5 fold increase in the expression level in cells growing on CMM.

Conclusion

Ornithine carbamoyltransferase and cystathionine beta-lyase were over-expressed in cells grown on cooked meat medium and also identified in the surface protein fraction and the former was immunogenic; making them potential vaccine candidates. Based upon bioinformatic analysis; choloylglycine hydrolase family protein, cell wall-associated serine proteinase, and rhomboid family protein were predicted as surface protein markers for specific detection of C. perfringens from the environment and food. Most of the proteins over-expressed in CMM were shown to have putative function in metabolism, of which seven were involved in amino acid transport and metabolism or lipid metabolism.

Recombinant Bacillus subtilis expressing the Clostridium perfringens alpha toxoid is a candidate orally delivered vaccine against necrotic enteritis

Recombinant Bacillus subtilis endospores have been used to vaccinate against tetanus and anthrax. In this work, we have developed spores that could be used to vaccinate against Clostridium perfringens alpha toxin and that could be used to protect against gas gangrene in humans and necrotic enteritis in poultry. The primary active agent in both cases is alpha toxin. A carboxy-terminal segment of the alpha toxin gene (cpa) fused to the glutathione-S-transferase (GST) gene was cloned in B. subtilis such that the encoded GST-Cpa(247-370) polypeptide had been expressed in the following three different ways: expression in the vegetative cell, expression on the surface of the spore coat (fused to the CotB spore coat protein), and a combined approach of spore coat expression coupled with expression in the vegetative cell. Mice immunized orally or nasally with three doses of recombinant spores that carried GST-Cpa(247-370) on the spore surface showed the most striking responses. This included seroconversion with anti-Cpa(247-370)-specific immunoglobulin G (IgG) responses in their sera, a Th2 bias, and secretory IgA responses in saliva, feces, and lung samples. Neutralizing IgG antibodies to alpha toxin were detected using in vitro and in vivo assays, and a toxin challenge established protection. Mice immunized nasally or orally with recombinant spores were protected against a challenge with 12 median lethal doses of alpha toxin. Existing use of spores as competitive exclusion agents in animal feeds supports their use as a potentially economical and heat-stable vaccine for the poultry industry.