Effects of Clostridium perfringens recombinant and crude phospholipase C and theta-toxin on rabbit hemodynamic parameters

Interaction of Macrophages and Cholesterol-Dependent Cytolysins: The Impact on Immune Response and Cellular Survival

Cholesterol-dependent cytolysins (CDCs) are key virulence factors involved in many lethal bacterial infections, including pneumonia, necrotizing soft tissue infections, bacterial meningitis, and miscarriage. Host responses to these diseases involve myeloid cells, especially macrophages. Macrophages use several systems to detect and respond to cholesterol-dependent cytolysins, including membrane repair, mitogen-activated protein (MAP) kinase signaling, phagocytosis, cytokine production, and activation of the adaptive immune system. However, CDCs also promote immune evasion by silencing and/or destroying myeloid cells. While there are many common themes between the various CDCs, each CDC also possesses specific features to optimally benefit the pathogen producing it. This review highlights host responses to CDC pathogenesis with a focus on macrophages. Due to their robust plasticity, macrophages play key roles in the outcome of bacterial infections. Understanding the unique features and differences within the common theme of CDCs bolsters new tools for research and therapy.

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.

Massive pneumatosis without necrosis: A case report of Clostridium perfringens sepsis in an extremely low birth weight infant

Pneumatosis intestinalis and free intraperitoneal air on abdominal radiographs are considered pathognomonic signs of necrotizing enterocolitis (NEC). We report a unique case of late-onset fulminant sepsis due to Clostridium perfringens presenting with shock, extensive pneumatosis intestinalis and free intraperitoneal air in an extremely low birth weight infant without histopathological evidence of bowel necrosis or NEC.

Perfringolysin O: The Underrated Clostridium perfringens Toxin?

The anaerobic bacterium Clostridium perfringens expresses multiple toxins that promote disease development in both humans and animals. One such toxin is perfringolysin O (PFO, classically referred to as θ toxin), a pore-forming cholesterol-dependent cytolysin (CDC). PFO is secreted as a water-soluble monomer that recognizes and binds membranes via cholesterol. Membrane-bound monomers undergo structural changes that culminate in the formation of an oligomerized prepore complex on the membrane surface. The prepore then undergoes conversion into the bilayer-spanning pore measuring approximately 250–300 Å in diameter. PFO is expressed in nearly all identified C. perfringens strains and harbors interesting traits that suggest a potential undefined role for PFO in disease development. Research has demonstrated a role for PFO in gas gangrene progression and bovine necrohemorrhagic enteritis, but there is limited data available to determine if PFO also functions in additional disease presentations caused by C. perfringens. This review summarizes the known structural and functional characteristics of PFO, while highlighting recent insights into the potential contributions of PFO to disease pathogenesis.

Cardiotoxicity during invasive pneumococcal disease

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia and sepsis, with adult hospitalization linked to approximately 19% incidence of an adverse cardiac event (e.g., heart failure, arrhythmia, infarction). Herein, we review the specific host-pathogen interactions that contribute to cardiac dysfunction during invasive pneumococcal disease: (1) cell wall-mediated inhibition of cardiomyocyte contractility; (2) the new observation that S. pneumoniae is capable of translocation into the myocardium and within the heart, forming discrete, nonpurulent, microscopic lesions that are filled with pneumococci; and (3) the bacterial virulence determinants, pneumolysin and hydrogen peroxide, that are most likely responsible for cardiomyocyte cell death. Pneumococcal invasion of heart tissue is dependent on the bacterial adhesin choline-binding protein A that binds to laminin receptor on vascular endothelial cells and binding of phosphorylcholine residues on pneumococcal cell wall to platelet-activating factor receptor. These are the same interactions responsible for pneumococcal translocation across the blood-brain barrier during the development of meningitis. We discuss these interactions and how their neutralization, either with antibody or therapeutic agents that modulate platelet-activating factor receptor expression, may confer protection against cardiac damage and meningitis. Considerable collagen deposition was observed in hearts of mice that had recovered from invasive pneumococcal disease. We discuss the possibility that cardiac scar formation after severe pneumococcal infection may explain why individuals who are hospitalized for pneumonia are at greater risk for sudden death up to 1 year after infection.

The synergistic necrohemorrhagic action of Clostridium perfringens perfringolysin and alpha toxin in the bovine intestine and against bovine endothelial cells

Bovine necrohemorrhagic enteritis is a major cause of mortality in veal calves. Clostridium perfringens is considered as the causative agent, but there has been controversy on the toxins responsible for the disease. Recently, it has been demonstrated that a variety of C. perfringens type A strains can induce necrohemorrhagic lesions in a calf intestinal loop assay. These results put forward alpha toxin and perfringolysin as potential causative toxins, since both are produced by all C. perfringens type A strains. The importance of perfringolysin in the pathogenesis of bovine necrohemorrhagic enteritis has not been studied before. Therefore, the objective of the current study was to evaluate the role of perfringolysin in the development of necrohemorrhagic enteritis lesions in calves and its synergism with alpha toxin. A perfringolysin-deficient mutant, an alpha toxin-deficient mutant and a perfringolysin alpha toxin double mutant were less able to induce necrosis in a calf intestinal loop assay as compared to the wild-type strain. Only complementation with both toxins could restore the activity to that of the wild-type. In addition, perfringolysin and alpha toxin had a synergistic cytotoxic effect on bovine endothelial cells. This endothelial cell damage potentially explains why capillary hemorrhages are an initial step in the development of bovine necrohemorrhagic enteritis. Taken together, our results show that perfringolysin acts synergistically with alpha toxin in the development of necrohemorrhagic enteritis in a calf intestinal loop model and we hypothesize that both toxins act by targeting the endothelial cells.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Life-threatening clostridial infections

Life-threatening soft tissue infections caused by Clostridium species have been described in the medical literature for hundreds of years largely because of their fulminant nature, distinctive clinical presentations and complex management issues. The Clostridium species perfringens, septicum and histolyticum are the principal causes of trauma-associated gas gangrene and their incidence increases dramatically in times of war, hurricanes, earthquakes and other mass casualty conditions. Recently, there has also been an increased incidence of spontaneous gas gangrene caused by Clostridium septicum in association with gastrointestinal abnormalities and neutropenia. Similarly, over the last 15 years there has been increased recognition of a toxic shock-like syndrome associated with Clostridium sordellii in individuals skin-popping black tar heroin, in women undergoing childbirth or other gynecologic procedures including medically-induced abortion. Like their cousins Clostridium tetanus and Clostridium botulinum, the pathogenesis of these clostridial infections is largely the consequence of potent exotoxin production. Strategies to inhibit toxin production, neutralize circulating toxins and prevent their interaction with cells of the innate immune response are sorely needed. Recent studies have elucidated novel targets that may hold promise for newer therapeutic modalities.

Necrotizing soft-tissue infections

OBJECTIVE

To provide a contemporary review of the diagnosis and management of necrotizing soft-tissue infections.

DATA SOURCES

Scientific literature and internet sources.

STUDY SELECTION

Major articles of importance in this area.

CONCLUSIONS

The mortality for necrotizing soft-tissue infections appears to be decreasing, possibly due to improved recognition and earlier delivery of more effective therapy. Establishing a diagnosis and initiating treatment as soon as possible provides the best opportunity for a good outcome.

Role of Clostridium perfringens phospholipase C in the pathogenesis of gas gangrene

Gas gangrene is an acute and devastating infection most frequently caused by Clostridium perfringens and characterized by severe myonecrosis, intravascular leukocyte accumulation, and significant thrombosis. Several lines of evidence indicate that C. perfringens phospholipase C (Cp-PLC), also called alpha-toxin, is the major virulence factor in this disease. This toxin is a Zn2+ metalloenzyme with lecithinase and sphingomyelinase activities. Its three dimensional structure shows two domains, an N-terminal domain which contains the active site, and a C-terminal domain required for the Ca2+dependent interaction with membranes. Cp-PLC displays several biological activities: it increases capillary permeability, induces platelet aggregation, hemolysis, myonecrosis, decreases cardiac contractility, and is lethal. Experiments with genetically engineered Cp-PLC variants have revealed that the sphingomyelinase activity and the C-terminal domain are required for toxicity. The myotoxicity of Cp-PLC is largely dependent on its membrane damaging effect. In addition, it has been suggested that the alterations in the blood flow induced by this toxin also contribute to muscle damage. In gas gangrene, Cp-PLC dysregulates transduction pathways in endothelial cells, platelets and neutrophils leading to the uncontrolled production of several intercellular mediators and adhesion molecules. Thus, Cp-PLC alters the traffic of neutrophils to the infected tissue and promotes thrombotic events, enhancing the conditions for anaerobic growth.

Multiple effects on Clostridium perfringens binding, uptake and trafficking to lysosomes by inhibitors of macrophage phagocytosis receptors

Clostridium perfringens is a Gram-positive, anaerobic bacterium that is the most common cause of gas gangrene (clostridial myonecrosis) in humans. C. perfringens produces a variety of extracellular toxins that are thought to be the major virulence factors of the organism. However, C. perfringens has recently been shown to have the ability to survive in a murine macrophage-like cell line, J774-33, even under aerobic conditions. In J774-33 cells, C. perfringens can escape the phagosome and gain access to the cytoplasm. Since the receptor that is used for phagocytosis can determine the fate of an intracellular bacterium, we used a variety of inhibitors of specific receptors to identify those used by J774-33 cells to phagocytose C. perfringens. It was found that the scavenger receptor and mannose receptor(s) were involved in the phagocytosis of C. perfringens. In the presence of complement, the complement receptor (CR3) was also involved in the binding and/or uptake of C. perfringens. Since the receptor inhibition studies indicated that the scavenger receptor played a major role in phagocytosis, C. perfringens binding studies were performed with a Chinese hamster ovary (CHO) cell line expressing the mouse SR-A receptor. The cell line expressing the SR-A receptor showed a significant increase in C. perfringens binding in comparison to the non-transfected CHO cells. In the absence of opsonizing antibodies, the Fc receptor was not used to phagocytose C. perfringens. Forcing the macrophages to use a specific receptor by using combinations of different receptor inhibitors led to only a slight increase in co-localization of intracellular C. perfringens with the late endosome-lysosome marker LAMP-1. Carbohydrate analysis of C. perfringens strain 13 extracellular polysaccharide confirmed the presence of mannose and negatively charged residues of glucuronic acid, which may provide the moieties that promote binding to the mannose and scavenger receptors, respectively.

Clostridium sordellii phospholipase C: gene cloning and comparison of enzymatic and biological activities with those of Clostridium perfringens and Clostridium bifermentans phospholipase C

The gene encoding Clostridium sordellii phospholipase C (Csp) was cloned and expressed as a histidine-tagged (His-tag) protein, and the protein was purified to compare its enzymatic and biological activities with those of Clostridium perfringens phospholipase C (Cpa) and Clostridium bifermentans phospholipase C (Cbp). Csp was found to consist of 371 amino acid residues in the mature form and to be more homologous to Cbp than to Cpa. The egg yolk phospholipid hydrolysis activity of the His-tag Csp was about one-third of that of His-tag Cpa, but the hemolytic activity was less than 1% of that of His-tag Cpa. His-tag Csp was nontoxic to mice. Immunization of mice with His-tag Cbp or His-tag Csp did not provide effective protection against the lethal activity of His-tag Cpa. These results indicate that Csp possesses similar molecular properties to Cbp and suggest that comparative analysis of toxic and nontoxic clostridial phospholipases is helpful for characterization of the toxic properties of clostridial phospholipases.

The role of clostridial toxins in the pathogenesis of gas gangrene

Clostridium perfringens gas gangrene is, without a doubt, the most fulminant necrotizing infection that affects humans. In victims of traumatic injury, the infection can become well established in as little as 6-8 h, and the destruction of adjacent healthy muscle can progress several inches per hour despite appropriate antibiotic coverage. Shock and organ failure are present in 50% of patients and, among these, 40% die. Despite modern medical advances and intensive-care regimens, radical amputation remains the single best life-saving treatment. Over the past century, much has been learned about the pathogenesis of this disease, and novel therapies are on the horizon for patients with this devastating infection.

The anaerobic pathogen Clostridium perfringens can escape the phagosome of macrophages under aerobic conditions

Clostridium perfringens is the most common cause of gas gangrene (clostridial myonecrosis), a disease that begins when ischaemic tissues become contaminated with C. perfringens vegetative cells or spores. An aerotolerant anaerobe, C. perfringens quickly multiplies in ischaemic tissues and spreads to healthy areas, leading to a high level of morbidity and mortality. As a species, the bacterium can synthesize 13 different toxins, and these are thought to be the major virulence factors of the disease. However, we present evidence here that C. perfringens can also persist inside macrophages, under aerobic conditions, by escaping the phagosome into the cytoplasm. C. perfringens was not killed by the cells of a clone (J774-33) of the macrophage-like murine cell line J774A.1 under aerobic or anaerobic conditions, whereas the non-pathogenic bacterium Bacillus subtilis was killed by J774-33 cells under both conditions. Electron microscopy images showed that C. perfringens cells were intact and resided mostly in the cytoplasm of J774-33 cells, whereas B. subtilis was in the phagosome. Immunofluorescence microscopy showed that intracellular C. perfringens bacteria failed to co-localize with the late endosome-lysosomal marker glycoprotein LAMP-1, whereas B. subtilis did co-localize with LAMP-1. C. perfringens also appeared to escape the phagosome of both activated and unactivated mouse peritoneal macrophages, but not as efficiently as was seen with the J774-33 cell line. In addition, cytochalasin D was used to show that phagocytosis of C. perfringens was dependent on actin polymerization and that the bacteria attach to J774-33 cells at distinct areas of the cell membrane. We propose that the ability to escape the phagosome and persist inside macrophages is an important factor in the early stages of a gangrene infection, when bacterial numbers are low and phagocytic cells are present.

The pathogenesis of clostridial myonecrosis

These pieces of evidence can be assimilated into a molecular and cellular model of pathogenesis which is initiated by direct toxin effects upon venous capillary endothelial cell function, leading to expression of pro-inflammatory mediators and adhesion molecules, and initiation of platelet aggregation. Toxin-induced hyperadhesion of leukocytes (see above section) with enhanced respiratory burst activity (due to toxins directly or to toxin-induced IL-8 or PAF synthesis by host cells) and toxin-induced chemotaxis deficits could result in neutrophil-mediated vascular injury. Direct toxin-induced cytopathic effects on EC may also contribute to vascular abnormalities associated with gas gangrene. Over prolonged incubation periods, PLC at sublytic concentrations causes EC to undergo profound shape changes similar to those described following prolonged TNF or interferon gamma exposure. In vivo, conversion of EC to this fibroblastoid morphology could contribute to the localized vascular leakage and massive swelling observed clinically with this infection. Similarly, the direct cytotoxicity of PFO could disrupt endothelial integrity and contribute to progressive edema both locally and systemically. Thus, via the mechanisms outlined above, both PLC and PFO may cause local, regional and systemic vascular dysfunction. For instance, local absorption of exotoxins within the capillary beds could affect the physiological function of the endothelium lining the postcapillary venules, resulting in impairment of phagocyte delivery at the site of infection. Toxin-induced endothelial dysfunction and microvascular injury could also cause loss of albumin, electrolytes, and water into the interstitial space resulting in marked localized edema. These events, combined with intravascular platelet aggregation and leukostasis, would increase venous pressures and favor further loss of fluid and protein in the distal capillary bed. Ultimately, a reduced arteriolar flow would impair oxygen delivery thereby attenuating phagocyte oxidative killing and facilitating anaerobic glycolysis of muscle tissue. The resultant drop in tissue pH, together with reduced oxygen tension, might further decrease the redox potential of viable tissues to a point suitable for growth of this anaerobic bacillus. As infection progresses and additional toxin is absorbed, larger venous channels would become affected, causing regional vascular compromise, increased compartment pressures and rapid anoxic necrosis of large muscle groups. When toxins reach arterial circulation, systemic shock and multiorgan failure rapidly ensue, and death is common.

Differences in the carboxy-terminal (Putative phospholipid binding) domains of Clostridium perfringens and Clostridium bifermentans phospholipases C influence the hemolytic and lethal properties of these enzymes

The phospholipases C of C. perfringens (alpha-toxin) and C. bifermentans (Cbp) show >50% amino acid homology but differ in their hemolytic and toxic properties. We report here the purification and characterisation of alpha-toxin and Cbp. The phospholipase C activity of alpha-toxin and Cbp was similar when tested with phosphatidylcholine in egg yolk or in liposomes. However, the hemolytic activity of alpha-toxin was more than 100-fold that of Cbp. To investigate whether differences in the carboxy-terminal domains of these proteins were responsible for differences in the hemolytic and toxic properties, a hybrid protein (NbiCalpha) was constructed comprising the N domain of Cbp and the C domain of alpha-toxin. The hemolytic activity of NbiCalpha was 10-fold that of Cbp, and the hybrid enzyme was toxic. These results confirm that the C-terminal domain of these proteins confers different properties on the enzymatically active N-terminal domain of these proteins.

The Clostridium perfringensα-toxin

The gene encoding the alpha-(cpa) is present in all strains of Clostridium perfringens, and the purified alpha-toxin has been shown to be a zinc-containing phospholipase C enzyme, which is preferentially active towards phosphatidylcholine and sphingomyelin. The alpha-toxin is haemolytic as a result if its ability to hydrolyse cell membrane phospholipids and this activity distinguishes it from many other related zinc-metallophospholipases C. Recent studies have shown that the alpha-toxin is the major virulence determinant in cases of gas gangrene, and the toxin might play a role in several other diseases of animals and man as diverse as necrotic enteritis in chickens and Crohn's disease in man. In gas gangrene the toxin appears to have three major roles in the pathogenesis of disease. First, it is able to cause mistrafficking of neutrophils, such that they do not enter infected tissues. Second, the toxin is able to cause vasoconstriction and platelet aggregation which might reduce the blood supply to infected tissues. Finally, the toxin is able to detrimentally modulate host cell metabolism by activating the arachidonic acid cascade and protein kinase C. The molecular structure of the alpha-toxin reveals a two domain protein. The amino-terminal domain contains the phospholipase C active site which contains zinc ions. The carboxyterminal domain is a paralogue of lipid binding domains found in eukaryotes and appears to bind phospholipids in a calcium-dependent manner. Immunisation with the non-toxic carboxyterminal domain induces protection against the alpha-toxin and gas gangrene and this polypeptide might be exploited as a vaccine. Other workers have exploited the entire toxin as the basis of an anti-tumour system.

Phospholipase C and perfringolysin O from Clostridium perfringens upregulate endothelial cell-leukocyte adherence molecule 1 and intercellular leukocyte adherence molecule 1 expression and induce interleukin-8 synthesis in cultured human umbilical vein endothelial cells

Clostridium perfringens phospholipase C (PLC) and perfringolysin O (PFO) differentially induced human umbilical vein endothelial cell expression and synthesis of endothelial cell-leukocyte adherence molecule-1 (ELAM-1), intracellular leukocyte adherence molecule-1 (ICAM-1), and interleukin-8 (IL-8). PLC strongly induced expression of ELAM-1, ICAM-1, and IL-8, while PFO stimulated early ICAM-1 expression but did not promote ELAM-1 expression or IL-8 synthesis. PLC caused human umbilical vein endothelial cells to assume a fibroblastoid morphology, whereas PFO, in high concentrations or after prolonged low-dose toxin exposure, caused cell death. The toxin-induced expression of proadhesive and activational proteins and direct cytopathic effects may contribute to the leukostasis, vascular compromise, and capillary leak characteristics of C. perfringens gas gangrene.