Purification and characterization of alpha-toxin produced by Clostridium novyi type A

Clostridioides difficile: Current overview and future perspectives

The most common world-wide cause of antibiotic-associated infectious diarrhea and colitis is the toxin producing bacterium, Clostridioides difficile (C. difficile). Here we review the background and characteristics of the bacterium and the toxins produced together with the epidemiology and the complex pathogenesis that leads to a broad clinical spectrum of disease. The review describes the difficulties faced in obtaining a quick and accurate diagnosis despite the range of sensitive and specific diagnostic tools available. We also discuss the problem of disease recurrence and the importance of disease prevention. The high rates of infection recurrence mean that treatment strategies are constantly under review and we outline the diverse treatment options that are currently in use and explore the emerging treatment options of pulsed antibiotic use, microbial replacement therapies and the use of monoclonal antibodies. We summarize the future direction of treatment strategies which include the development of novel antibiotics, the administration of oral polyclonal antibody formulations, the use of vaccines, the administration of competitive non-toxigenic spores and the neutralization of antibiotics at the microbiota level. Future successful treatments will likely involve a combination of therapies to provide the most effective and robust approach to C. difficile management.

Vaccine Production to Protect Animals Against Pathogenic Clostridia

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

Adhesion and invasion of Clostridium perfringens type A into epithelial cells

Clostridium perfringens is the causative agent for necrotic enteritis. It secretes the major virulence factors, and α- and NetB-toxins that are responsible for intestinal lesions. The TpeL toxin affects cell morphology by producing myonecrosis, but its role in the pathogenesis of necrotic enteritis is unclear. In this study, the presence of netB and tpeL genes in C. perfringens type A strains isolated from chickens with necrotic enteritis, their cytotoxic effects and role in adhesion and invasion of epithelial cells were evaluated. Six (27.3%) of the 22 C. perfringens type A strains were harboring the tpeL gene and produced morphological alterations in Vero cells after 6 h of incubation. Strains tpeL (−) induced strong cell rounding after 6 h of incubation and produced cell enlargement. None of the 22 strains harbored netB gene. All the six tpeL (+) gene strains were able to adhere to HEp-2 cells; however, only four of them (66.6%) were invasive. Thus, these results suggest that the presence of tpeL gene or TpeL toxin might be required for the adherence of bacteria to HEp-2 cells; however, it could not have any role in the invasion process.

View from the front lines: an emergency medicine perspective on clostridial infections in injection drug users

Injection drug use (IDU), specifically non-intravenous "skin-popping" of heroin, seems to provide optimal conditions for Clostridial infection and toxin production. IDU is therefore a major risk factor for wound botulism and Clostridial necrotizing soft tissue infections (NSTI) and continues to be linked to cases of tetanus. Case clusters of all 3 diseases have occurred among IDUs in Western U.S. and Europe. Medical personnel who care for the IDU population must be thoroughly familiar with the clinical presentation and management of these diseases. Wound botulism presents with bulbar symptoms and signs that are easily overlooked; rapid acquisition and administration of antitoxin can prevent neuromuscular respiratory failure. In addition to Clostridium perfringens, IDU-related NSTIs can be caused by Clostridium sordellii and Clostridium novyi, which may share a distinct clinical presentation. Early definitive NSTI management, which decreases mortality, requires a low index of suspicion on the part of emergency physicians and low threshold for surgical exploration and debridement on the part of the surgeon. Tetanus should be preventable in the IDU population through careful attention to vaccination status.

Toward a structural understanding of Clostridium difficile toxins A and B

Clostridium difficile is a toxin-producing bacterium that is a frequent cause of hospital-acquired and antibiotic-associated diarrhea. The incidence, severity, and costs associated with C. difficile associated disease are substantial and increasing, making C. difficile a significant public health concern. The two primary toxins, TcdA and TcdB, disrupt host cell function by inactivating small GTPases that regulate the actin cytoskeleton. This review will discuss the role of these two toxins in pathogenesis and the structural and molecular mechanisms by which they intoxicate cells. A focus will be placed on recent publications highlighting mechanistic similarities and differences between TcdA, TcdB, and different TcdB variants.

Padronização de teste de Potência in vitro Para vacinas que contenham toxoide alfa de Clostridium novyi tipo B

RESUMO Clostridium novyi tipo B é o patógeno responsável pela hepatite necrótica, causada pela ação da toxina alfa. O controle desta enfermidade é baseado na imunização dos animais com vacinas que contenham na sua composição toxóide alfa de C. novyi tipo B. O teste de potência deste imunógeno é realizado a partir de soros de coelhos imunizados, por meio da técnica de soroneutralização em camundongos. Portanto objetivou-se padronizar um teste de potência de toxóide alfa de C. novyi tipo B em linhagem de célula VERO, como método alternativo ao bioensaio animal. O coeficiente de correlação obtido pelas técnicas in vitro e in vivo foi de 98,38%, indicando ser possível a utilização do modelo estudado na substituição do modelo animal para teste de potência de toxoide alfa de C. novyi tipo B.

A novel toxin homologous to large clostridial cytotoxins found in culture supernatant of Clostridium perfringens type C

An unknown cytotoxin was identified in the culture supernatant of Clostridium perfringens type C. The cytotoxin, named TpeL, which was purified using mAb-based affinity chromatography, had a lethal activity of 62 minimum lethal dose (MLD) mg(-1) in mice and a cytotoxic activity of 6.2x10(5) cytotoxic units (CU) mg(-1) in Vero cells. The nucleotide sequence of TpeL was determined. The entire ORF had a length of 4953 bases, and the same nucleotide sequence was not recorded in the GenBank/EMBL/DDBJ databases. The molecular mass calculated from the deduced amino acid sequence was 191 kDa, and a signal peptide region was not found within the ORF. The deduced amino acid sequence exhibited 30-39 % homology to Clostridium difficile toxins A (TcdA) and B (TcdB), Clostridium sordellii lethal toxin (TcsL) and Clostridium novyi alpha-toxin (TcnA). The amino acid sequence of TpeL is shorter than these toxins, and the homologous region was located at the N-terminal site. Eighteen strains of C. perfringens types A, B and C were surveyed for the presence of the tpeL gene by PCR. The tpeL gene was detected in all type B (one strain) and C strains (five strains), but not in any type A strains (12 strains). TpeL was detected in culture filtrates of the five type C strains by dot-blot analysis, but not in the type B strain. It was concluded that TpeL is a novel toxin similar to the known large clostridial cytotoxins. Furthermore, the data indicated that TpeL is produced by many C. perfringens type C strains.

Development of a cell culture assay for the quantitative determination of vaccination-induced antibodies in rabbit sera against Clostridium perfringens epsilon toxin and Clostridium novyi alpha toxin

Cell culture assays are possible alternatives to replace in vivo neutralization tests currently required for potency testing of clostridial vaccines. Cell culture assays based on the MDCK cell line and the Vero cell line which are sensitive to the Clostridium (C.) perfringens type D epsilon toxin and Clostridium novyi type B alpha toxin, respectively, were developed, and the test conditions were standardized. The antibody titres of vaccinated rabbits measured in vitro were compared with the results of current test procedures recommended by European Pharmacopoeia. The correlation coefficients calculated were significant for all sera tested. The cell culture assays proved to be sensitive, specific, reproducible and reliable. Therefore, these cell culture assays could be suitable in vitro alternatives to the in vivo mouse neutralization experiments required for potency tests of clostridial vaccines, but further validation studies are necessary.

Clostridial Rho-inhibiting protein toxins

Rho proteins are master regulators of a large array of cellular functions, including control of cell morphology, cell migration and polarity, transcriptional activation, and cell cycle progression. They are the eukaryotic targets of various bacterial protein toxins and effectors, which activate or inactivate the GTPases. Here Rho-inactivating toxins and effectors are reviewed, including the families of large clostridial cytotoxins and C3-like transferases, which inactivate Rho GTPases by glucosylation and ADP-ribosylation, respectively.

Bacterial toxins that modify the actin cytoskeleton

Bacterial pathogens utilize several strategies to modulate the organization of the actin cytoskeleton. Some bacterial toxins catalyze the covalent modification of actin or the Rho GTPases, which are involved in the control of the actin cytoskeleton. Other bacteria produce toxins that act as guanine nucleotide exchange factors or GTPase-activating proteins to modulate the nucleotide state of the Rho GTPases. This latter group of toxins provides a temporal modulation of the actin cytoskeleton. A third group of bacterial toxins act as adenylate cyclases, which directly elevate intracellular cAMP to supra-physiological levels. Each class of toxins gives the bacterial pathogen a selective advantage in modulating host cell resistance to infection.

Protective effects of clostridium sordellii LT and HT toxoids against challenge with spores in guinea pigs

The protective effects of Clostridium sordellii lethal toxin (LT) and hemorrhagic toxin (HT) toxoids against challenge with spores in guinea pigs were investigated. Purified LT and partially purified HT were obtained from the culture supernatant of C. sordellii strain 3703, and then were treated with formalin to make toxoids. LT. HT and combined LT and HT (LT/HT) toxoid vaccines were prepared by mixing each toxoid with an aluminum phosphate gel as adjuvant. Guinea pigs immunized twice with the respective toxoid vaccines were challenged with spores of strains 3703 or KZ1047. The latter strain does not produce HT. LT toxoid vaccine conferred protection against challenge with strain KZ1047, but not strain 3703, in guinea pigs. All guinea pigs immunized with HT toxoid vaccine died after challenge with spores of either strain. LT/HT toxoid vaccine gave complete protection against challenge with spores of strains 3703 and KZ1047 to guinea pigs. These results suggest that not only LT toxoid, but also HT toxoid, are essential protective antigens of C. sordellii.

pH-induced conformational changes in Clostridium difficile toxin B

Toxin B from Clostridium difficile is a monoglucosylating toxin that targets substrates within the cytosol of mammalian cells. In this study, we investigated the impact of acidic pH on cytosolic entry and structural changes within toxin B. Bafilomycin A1 was used to block endosomal acidification and subsequent toxin B translocation. Cytopathic effects could be completely blocked by addition of bafilomycin A1 up to 20 min following toxin treatment. Furthermore, providing a low extracellular pH could circumvent the effect of bafilomycin A1 and other lysosomotropic agents. Acid pH-induced structural changes were monitored by using the fluorescent probe 2-(p-toluidinyl) naphthalene-6-sulfonic acid, sodium salt (TNS), inherent tryptophan fluorescence, and relative susceptibility to a specific protease. As the toxin was exposed to lower pH there was an increase in TNS fluorescence, suggesting the exposure of hydrophobic domains by toxin B. The change in hydrophobicity appeared to be reversible, since returning the pH to neutrality abrogated TNS fluorescence. Furthermore, tryptophan fluorescence was quenched at the acidic pH, indicating that domains may have been moving into more aqueous environments. Toxin B also demonstrated variable susceptibility to Staphylococcus aureus V8 protease at neutral and acidic pH, further suggesting pH-induced structural changes in this protein.

Cytotoxic activity of coagulase-negative staphylococci in bovine mastitis

Secreted toxins play important roles in the pathogenesis of bacterial infections. In this study, we examined the presence of secreted cytotoxic factors of coagulase-negative staphylococci (CoNS) from bovine clinical and subclinical mastitis. A 34- to 36-kDa protein with cell-rounding cytotoxic activity was found in many CoNS strains, especially in Staphylococcus chromogenes strains. The protein caused cell detachment and cell rounding in several cell lines, including HEp-2, Int 407, CHO-K1, and Y-1 cells. Native protein recovered from nondenatured polyacrylamide gel electrophoresis showed both cytotoxic activity and casein hydrolysis activity. The purified protein had a pH optimal at 7.2 to 7.5 and a pI of 5.1 and was heat labile. The proteolytic activity could be inhibited by zinc and metal specific inhibitors such as 1, 10-phenanthroline and EDTA, indicating that it is a metalloprotease. Protein mass analysis and peptide sequencing indicated that the protein is a novel metalloprotease. Different bacterial strains expressed variable levels of 34- to 36-kDa protease, which may provide an indication of strain virulence.

Detection of Clostridium novyi type B alpha toxin by cell culture systems

Ten permanent cell lines were examined for their reaction to the Clostridium novyi alpha toxin. The action of the toxin was determined after 3 days by microscopic examination and the MTT assay. The alpha toxin exhibited the strongest effect on ESH-L cells rather than other cell lines. Vero and SFT-R cells reacted in a comparable way, but less sensitively. We were able to show that the cytopathic effect on the three types of cells was neutralised by the international standard for gas gangrene antitoxin (C. novyi) but in no case by heterologous antisera. Our results have shown that the three cell lines were specific indicators for the detection of the cytopathic effect of alpha toxin. The cytopathic effect can be measured reproducibly by the cell culture assay used. These results are suitable as the starting point for the development of the neutralisation test using cell cultures.

The protective effect of Clostridium novyi type B alpha-toxoid against challenge with spores in guinea pigs

Clostridium novyi (C. novyi) Type B alpha-toxin was purified from culture supernatant by column chromatography, and was inactivated by formalin. A purified alpha-toxoid vaccine was prepared by mixing it with an aluminum phosphate gel adjuvant. Guinea pigs immunized twice with 4 micrograms or more of alpha-toxin survived against challenge with C. novyi Type B spores. Anti-alpha-toxin (antitoxin) titer was measured by toxin neutralization test using Vero cells. All of the guinea pigs having antitoxin titers of 10 units (U) or more at challenge were survived. In another experiment, guinea pigs were immunized with crude alpha-toxoid vaccines prepared by inactivated culture supernatant or by adding broken bacterial cells to the former. In this experiment, 10 U of antitoxin titer was the border of survival or death after challenge. Guinea pigs with antitoxin titers of less than 5 U, 5 U and 10 U died at 2, 3 to 4 and 4 days, respectively, after challenge. These results suggest that C. novyi alpha-toxin was the main protective antigen against challenge exposure to spores in guinea pigs.

Identification and partial characterization of an Actinomyces pyogenes hemolysin

Twenty-two Actinomyces pyogenes isolates were recovered from hepatic abscesses in cattle and evaluated for hemolysin production. Hemolysin was collected from supernatant of cultures grown in 6% CO2 in brain heart infusion (BHI) broth. The effect of oxidizing and reducing agents, enzymes, temperatures and pH on hemolytic activity were studied using sheep erythrocytes as the target cells. Our study showed that A. pyogenes hemolysin is oxygen stable; sensitive to treatment by protease, trypsin, and amylase; and destroyed by treatment at extreme temperatures (56 and 100 degrees C) and pH (pH 3 and 11). Production of hemolysin was studied in BHI, RPMI-1640, and a defined serum-free A. pyogenes medium under aerobic and anaerobic conditions. Maximum hemolysin was produced in BHI incubated aerobically in 6% CO2 and to a lesser degree anaerobically in RPMI-1640. No hemolysin was produced in the defined A. pyogenes medium. Differential filtration, isoelectric focusing and sodium dodecyl sulfate polyacrylamide gel electrophoresis identified two hemolysin proteins with pI values of 3.40 and 9.45 and estimated molecular masses of 62 and 58 kDa, respectively. Cell-free supernatant samples positive for hemolysin activity also were screened for leukotoxin activity. Significant levels of leukotoxin were detected in all samples screened.