Virulence genes of Clostridium perfringens

Clostridium perfringens causes human gas gangrene and food poisoning as well as several enterotoxemic diseases of animals. The organism is characterized by its ability to produce numerous extracellular toxins including alpha-toxin or phospholipase C, theta-toxin or perfringolysin O, kappa-toxin or collagenase, as well as a sporulation-associated enterotoxin. Although the genes encoding the alpha-toxin and theta-toxin are located on the chromosome, the genes encoding many of the other extracellular toxins are located on large plasmids. The enterotoxin gene can be either chromosomal or plasmid determined. Several of these toxin genes are associated with insertion sequences. The production of many of the extracellular toxins is regulated at the transcriptional level by the products of the virR and virS genes, which together comprise a two-component signal transduction system.

Virulence studies on chromosomal alpha-toxin and theta-toxin mutants constructed by allelic exchange provide genetic evidence for the essential role of alpha-toxin in Clostridium perfringens-mediated gas gangrene

The pathogenesis of clostridial myonecrosis, or gas gangrene, involves the growth of the anaerobic bacterium Clostridium perfringens in the infected tissues and the elaboration of numerous extracellular toxins and enzymes. The precise role of each of these toxins in tissue invasion and necrosis has not been determined. To enable genetic approaches to be used to study C. perfringens pathogenesis we developed an allelic exchange method which involved the transformation of C. perfringens cells with a suicide plasmid carrying a gene insertionally inactivated with an erythromycin-resistance determinant. The frequency with which double reciprocal crossover events were observed was increased to a workable level by increasing the amount of homologous DNA located on either side of the inactivated gene. Allelic exchange was used to isolate mutations in the chromosomal pfoA gene, which encodes an oxygen-labile haemolysin known as theta-toxin or perfringolysin O, and in the chromosomal plc gene, which encodes the alpha-toxin or phospholipase C. The resultant mutants failed to produce detectable theta-toxin or alpha-toxin activity, respectively, and could be complemented by recombinant plasmids that carried the respective wild-type genes. The resultant strains were virulence tested in a mouse myonecrosis model. The results showed that the plc mutants had demonstrably reduced virulence and therefore provided definitive genetic evidence for the essential role of alpha-toxin in gas gangrene or clostridial myonecrosis.

Isolation of Clostridium in human infections: evaluation of 114 cases

One hundred fifty-two strains of Clostridium were isolated from 144 patients over a 14-month-peroid. These included 23 recognized species and 23 strains that were unclassified. Soft tissues or abscesses yielded 84 strains of Clostridium. Intraabdominal sites predominated, but clostridia were recovered from empyema, carcinoma, frostbite with gas gangrene, muscle abscess, aortic graft, and brain abscess. Blood cultures yielded 65 strains of Clostridium from 49 patients, representing 0.3% of 16,314 blood cultures (or 2.6% of 2,168 positive cultures). Clostridium perfringens was most common in blood, accounting for 37 isolates (57%). Clostridial bacteremia was often unrelated to the clinical setting and was found in alcoholics with aspiration or Streptococcus pneumoniae pneumonia, pulmonary tuberculosis, empyema, meningococcemia, and infantile gastroenteritis. In 20 of the 49 patients (41%), aerobic or other anaerobic bacteria were cultured concurrently from the blood. Thus, clostridial bacteremia should be interpreted with caution since there may be little correlation with the patient's clinical condition.

Gas gangrene

Gas gangrene is not a disease of the past. Despite improved awareness, earlier care of trauma victims, new antibiotics, and advanced monitoring techniques, histotoxic clostridia continue to cause loss of life and limb. A 20-year literature review on gas gangrene (Part I) indicates that a combined therapy approach with early recognition, surgical intervention, appropriate antibiotics, and hyperbaric oxygen (HBO) provides optimal care. Part II, a 15-year clinical experience, appears to be the largest English-language series reported using the combined therapy of antibiotics, surgery, and hyperbaric oxygen. One hundred thirty-nine patients (95 males and 44 females), average age, 38 years, were admitted with clostridial myonecrosis. Sixty-seven were in shock at admission and the 27 deaths occurred in this group. One hundred twelve patients (81%) survived the infection. There was a 5% mortality in post-traumatic extremity clostridial myonecrosis. Age and concurrent disease increased the mortality rate, as did delay from time of diagnosis to aggressive combined treatment.

Spontaneous, nontraumatic gangrene due to Clostridium septicum

Clostridium septicum is a major cause of spontaneous, nontraumatic gas gangrene. Unlike Clostridium perfringens, C. septicum is relatively aerotolerant and thus appears to be more capable of initiating infection in the absence of obvious damage to tissues. Six cases illustrate the clinical setting and fulminant nature of spontaneous gangrene caused by C. septicum. A lesion in the colon such as carcinoma is often present and is presumed to serve as a portal of entry to the bloodstream. Diabetes and leukopenia are also common predisposing conditions; compromise of vital host responses may facilitate proliferation of those organisms that settle out in the tissues. Acute lymphoma or leukemia during a course of chemotherapy is accompanied by damage to bowel mucosa and granulocytopenia, thus predisposing to spontaneous clostridial gangrene. Infection progresses in a fulminating manner; the majority of patients die within 24 hours of onset. Characteristic symptoms and signs include excruciating pain (although a sense of heaviness may be the only early symptom), swelling of tissues, crepitance, and bulla formation. A hallmark of C. septicum infection is the absence of acute inflammatory cells in involved tissues or in bulla fluid. A series of laboratory investigations demonstrated that fluid obtained from a bulla adversely affected the viability, morphology, and function of polymorphonuclear leukocytes (PMNs), which may explain the paucity of PMNs in involved tissues and may in part contribute to the fulminant progression observed in infection due to this organism.

Fulminant and fatal gas gangrene of the stomach in a healthy live liver donor

A 57-year-old male with a history of hypercholesterolemia and anxiety but otherwise in good health volunteered to donate the right lobe of his liver to his brother. The operation was performed uneventfully, without transfusion. Postoperatively he did well, until he developed tachycardia, profound hypotension, and coffee ground emesis on postoperative day 3. Despite resuscitative measures, he arrested and expired. Autopsy demonstrated gas gangrene of the stomach as the underlying cause of the hemorrhage and numerous colonies of Gram-positive bacilli were identified. Subsequent polymerase chain reaction (PCR) analysis identified these bacteria to be Clostridium perfringens (C. perfringens) type D. This patient's death was devastating, both to his family and his medical team. The impact of his death has transcended that of an individual occurrence. In conclusion, herein we present the facts and discuss this extraordinary example of florid clostridial infection and toxin-mediated shock. It was completely unexpected and probably unpreventable, and its cause was almost inconceivable.

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.

Gas gangrene and related infection: classification, clinical features and aetiology, management and mortality. A report of 88 cases

The clinical features of gas gangrene and related infection seen in 88 patients over a 10-year period are described. It is suggested that clostridial infection could be simply classified as either 'gas-forming' or 'non-gas-forming'. The gas-forming group represents the more severe form of infection. Non-clostridial gas gangrene may present in a variety of forms. The anaerobic streptococcus was the organism most frequently responsible, but these cases were indistinguishable from clostridial infection on clinical grounds. The treatment of gas gangrene in this series of patients is reported. Emphasis is laid on the importance of adequate prophylaxis with penicillin in patients at risk. The value of antibiotics in established infection remains equivocal. The evidence supporting the value of hyperbaric oxygen therapy is assessed and an attempt made to quantify the response to this treatment. Benefit was apparent in only a proportion of patients. A favourable response indicated clostridial infection and guaranteed immediate survival. Extensive debridement or amputation is unnecessary in this group. No response following hyperbaric oxygen therapy indicated widespread mixed clostridial and non-clostridial infection, or infection due to organisms other than clostridia. Urgent and extensive debridement and amputation remain the predominant measures in this group.

Fatal Clostridium perfringens sepsis from a pooled platelet transfusion

A male patient with acute myeloid leukaemia received a pooled platelet preparation prepared by Optipress system on the last day of its shelf life. The patient collapsed after two-thirds of the contents had been transfused. Clostridium perfringens was isolated from the platelet bag within 18 h of the acute event. Metronidazole, gentamicin and Clostridium antiserum were then administered in addition to the broad spectrum antibiotics started previously. However, the patient died 4 days after the platelets were transfused. The cause of death was given as cardiovascular shock, entirely compatible with an overwhelming bacteraemic and septic episode. A coroner's verdict of accidental death due to transfusion of a contaminated unit of platelets was recorded. On subsequent investigation Cl. perfringens type A serotype PS68,PS80 (identical to that found in the platelet bag) was cultured from the venepuncture site of the arm of one of the donors who contributed towards the platelet pool. The donor had two young children and frequently changed nappies. Faecal contamination of the venepuncture site was the suspected source for the transmission of Cl. perfringens, an organism commonly found in the soil and intestinal tract of humans. This case dramatically highlights the consequences of transfusing a bacterially contaminated unit. It is vital that such incidents are investigated and reported so that the extent of transfusion-associated bacterial transmission can be monitored and preventative measures taken if possible.

Use of genetically manipulated strains of Clostridium perfringens reveals that both alpha-toxin and theta-toxin are required for vascular leukostasis to occur in experimental gas gangrene

A hallmark of gas gangrene (clostridial myonecrosis) pathology is a paucity of leukocytes infiltrating the necrotic tissue. The cause of this paucity most likely relates to the observation of leukocyte aggregates at the border of the area of tissue necrosis, often within the microvasculature itself. Infecting mice with genetically manipulated strains of Clostridium perfringens type A (deficient in either alpha-toxin or theta-toxin production) resulted in significantly reduced leukocyte aggregation when alpha-toxin was absent and complete abrogation of leukocyte aggregation when theta-toxin was absent. Thus, both alpha-toxin and theta-toxin are necessary for the characteristic vascular leukostasis observed in clostridial myonecrosis.

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.

Clostridium septicum infections in children: a case report and review of the literature

Clostridium myonecrosis is a rare and deadly infection that progresses very rapidly; thus, prompt diagnosis and treatment is vital. In adults, clostridial myonecrosis used to be a well-known complication of war wounds. Today, it is usually seen in settings of trauma, surgery, malignancy, skin infections/burns, and septic abortions. More recently, cases of nontraumatic or spontaneous clostridial myonecrosis have been reported in both adults and children. Clostridium perfringens and Clostridium septicum are responsible for the majority of the clinically relevant infections. Higher mortality rates are seen when C septicum is the causative agent. Here we present a child who survived a severe case of C septicum myonecrosis involving both abdominal and thoracic cavities. This rare infection has a high mortality rate and might be easily misdiagnosed in children, even by experienced clinicians, because of its nonspecific presentation. We also review all reported pediatric cases of C septicum infection and myonecrosis and discuss the surgical and medical interventions associated with improved survival. We identified a total of 47 cases of C septicum infection; of these, 22 (47%) were cases of C septicum associated with myonecrosis. Several factors, if available, were analyzed for each case: age, gender, infection location, previous diagnoses, presenting signs and symptoms, neutropenia, gross pathology of the colon, antibiotic use, surgical intervention, and final outcome. We found that conditions related with C septicum infection in children can be grouped into 3 major categories: patients with neutrophil dysfunction; patients with associated bowel ischemia; and patients with a history of trauma. Malignancies were found in 49% of the cases, cyclic or congenital neutropenia in 21%, hemolytic-uremic syndrome in 11%, structural bowel ischemia in 4%, and local extremity trauma in 6%. In addition, 6% of the cases had no known underlying disorder. Abdominal symptoms including vomiting, diarrhea, blood per rectum, abdominal pain, anorexia, and/or acute abdomen, were reported in 85% of the children. Fever was also a common finding. The mainstay of treatment for C septicum infection was parenteral antibiotics and/or surgical intervention. The mortality rate for children with C septicum infection and myonecrosis was 57% and 59%, respectively. Although 82% of all cases received antibiotics, only 43% underwent therapeutic surgical intervention. Several clinical factors were found to be associated with improved survival. Only 35% of the children with gastrointestinal tract involvement survived, compared with 86% of the children without gastrointestinal tract involvement. The survival rates for other conditions ranged from 0% to 50%. One hundred percent survival was reported in patients with no previously diagnosed conditions and those with infections resulting from trauma to the extremities. All survivors received antibiotic treatment, compared with only 68% of the nonsurvivors. Most survivors (84%) underwent therapeutic surgical intervention, compared with only 12% of nonsurvivors. Other treatments were used adjunctively, including hyperbaric oxygen, granulocyte colony-stimulating factor, granulocyte transfusions, and intravenous immunoglobulin. C septicum infections in children are often fatal; thus, one needs to have a high index of suspicion in at-risk patients. This review describes who these patients are, their clinical presentation, and the therapeutic strategies associated with improved survival.

Clostridium perfringens phospholipase C-induced platelet/leukocyte interactions impede neutrophil diapedesis

Clostridium perfringens gas gangrene is a fulminant necrotizing infection in which inflammatory cells are notably absent from infected tissues but are often massed within adjacent vessels. It has been shown that C. perfringens phospholipase C (PLC) stimulates formation of large intravascular platelet/leukocyte complexes and that PLC-induced activation of platelet gpIIbIIIa plays a major role. In vivo, such aggregates contribute to microvascular thrombosis and ischaemic necrosis of tissue. However, the effects of adherent platelets on neutrophil diapedesis have not been established. The present work investigated (1) the contribution of platelet P-selectin (CD62P) to PLC-induced cellular complex formation and (2) the effects of platelet adhesion on neutrophil diapedesis. The effects of anti-gpIIbIIIa and anti-CD62P strategies on PLC-induced complex formation were measured by flow cytometry and followed by light microscopy. Both platelet gpIIbIIIa and CD62P contributed to the formation of platelet/leukocyte complexes. Specifically, gpIIbIIIa mediated the formation of large platelet/platelet aggregates that were tethered to the leukocyte principally via CD62P. Neutrophil diapedesis, quantified by a transendothelial cell migration assay and visualized by electron microscopy, was significantly reduced (>60%) by the adherence of large platelet aggregates. It was concluded that the absence of a tissue inflammatory response in C. perfringens gas gangrene is due, in part, to impaired neutrophil mobility caused by large aggregates of adherent platelets induced by PLC. Further, an adjunctive immunotherapeutic strategy targeting both gpIIbIIIa and CD62P may improve the tissue inflammatory response, prevent vascular occlusion, maintain tissue viability, and reduce the need for radical amputation in patients with clostridial gas gangrene.

Microbiology and management of soft tissue and muscle infections

This review summarizes the microbiological aspects and management of soft tissue and muscle infections. The infections presented are: impetigo, folliculitis, furunculosis and carbuncles, cellulitis, erysipelas, infectious gangrene (includes necrotizing fasciitis or streptococcal gangrene, gas gangrene or clostridium myonecrosis, anaerobic cellulites, progressive bacterial synergistic gangrene, synergistic necrotizing cellulitis or perineal phlegmon, gangrenous balanitis, and gangrenous cellulitis in the immunocompromised patient), secondary bacterial infections complication skin lesions, diabetic and other chronic superficial skin ulcers and subcutaneous abscesses and myositis. These infections often occur in body sites or in those that have been compromised or injured by foreign body, trauma, ischemia, malignancy or surgery. In addition to Group A streptococci and Staphylococcus aureus, the indigenous aerobic and anaerobic cutaneous and mucous membranes local microflora usually is responsible for polymicrobial infections. These infections may occasionally lead to serious potentially life-threatening local and systemic complications. The infections can progress rapidly and early recognition and proper medical and surgical management is the cornerstone of therapy.

Necrotising enterocolitis of the newborn--is it gas-gangrene of the bowel?

Necrotising enterocolitis (N.E.C.) of the newborn is thought to be caused by ischaemia of the bowel. This would favour the conversion of clostridial spores, which can occur very early in the intestinal tract of newborns, to toxin-producing, invading bacilli. The histology of resected gut specimens from 6 of 7 N.E.C. patients who had undergone operation was similar to that in cases of gas-gangrene of the bowel and that in experimentally provoked pneumatosis cystoides intestinalis. In one case Clostridium perfringens type A was cultured in great number by anaerobic technique. The clostridia in these cases may have played an important role in the development of N.E.C.

Identification of residues critical for toxicity in Clostridium perfringens phospholipase C, the key toxin in gas gangrene

Clostridium perfringens phospholipase C (PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. The toxic activities of genetically engineered alpha-toxin variants harboring single amino-acid substitutions in three loops of its C-terminal domain were studied. The substitutions were made in aspartic acid residues which bind calcium, and tyrosine residues of the putative membrane-interacting region. The variants D269N and D336N had less than 20% of the hemolytic activity and displayed a cytotoxic potency 103-fold lower than that of the wild-type toxin. The variants in which Tyr275, Tyr307, and Tyr331 were substituted by Asn, Phe, or Leu had 11-73% of the hemolytic activity and exhibited a cytotoxic potency 102- to 105-fold lower than that of the wild-type toxin. The results demonstrated that the sphingomyelinase activity and the C-terminal domain are required for myotoxicity in vivo and that the variants D269N, D336N, Y275N, Y307F, and Y331L had less than 12% of the myotoxic activity displayed by the wild-type toxin. This work therefore identifies residues critical for the toxic activities of C. perfringens PLC and provides new insights toward understanding the mechanism of action of this toxin at a molecular level.

Infection and musculoskeletal conditions: Infectious myositis

Infectious myositis, an infection of the skeletal muscle(s), is uncommon. This clinical entity may be caused by viral, bacterial, fungal, and parasitic pathogens. Viral etiologies typically cause diffuse myalgias and/or myositis, whereas bacteria and fungi usually lead to a local myositis which may be associated with sites compromised by trauma or surgery and are more common among immunocompromised patients. Localized collections within the muscles are referred to as pyomyositis. Other pyogenic causes of myositis include gas gangrene, group A streptococcal myonecrosis, and other types of non-clostridial myonecrosis. Early recognition and treatment of these conditions are necessary as they may rapidly become life-threatening.

Nontraumatic clostridial myonecrosis

We describe three cases of nontraumatic clostridial myonecrosis seen at the Victorian Institute of Forensic Medicine. Nontraumatic clostridial myonecrosis is an uncommon and often fatal condition that requires immediate institution of appropriate medical and surgical therapy. It is most commonly caused by Clostridium perfringens and Clostridium septicum and is associated with gastrointestinal and hematologic malignancies, diabetes mellitus, and peripheral vascular disease. The clinical features include a rapidly evolving acute illness with severe pain, marked tachycardia, and brawny discoloration of the skin with bullae formation and crepitus, followed by hypotension and acute renal failure. Features at autopsy include reddish brown skin discoloration with bullae formation and necrotic skeletal muscle. Radiographs may be of use prior to the postmortem in detecting gas within the soft tissues. Gram stain and microbiologic culture are important in establishing a definitive diagnosis; although the major factors in suggesting the diagnosis are the recognition of the typical clinical history and macroscopic autopsy findings.

Postoperative clostridial infections in Britain

Eighty-five cases of clostridial infection, including 56 cases of gas gangrene, followed "clean" surgical operations performed in British hospitals in the course of two years. Nearly all the serious infections followed amputations of the leg for ischaemia or other operations on the leg in which a foreign body was implanted. All the infections were sporadic, and the evidence suggested that the infecting organism usually came from the bowel of the patient. Nearly half of the operations were performed in modern theatres with satisfactory ventilation and unexceptionable arrangements for the sterilization of instruments and dressings.Skin sterilization was often carried out perfunctorily or with agents with poor sporicidal activity. Total eradication of spores from the skin is, however, difficult to achieve, and recontamination may occur during the operation. Hence it is considered justifiable to give penicillin prophylactically to the small group of patients at serious risk from postoperative gas gangrene.

Clostridium perfringens alpha-toxin induces rabbit neutrophil adhesion

Clostridium perfringens alpha-toxin, which is one of the main agents involved in the development of gas gangrene, stimulates O(2)(-)production in neutrophils. Exposure of rabbit neutrophils to the alpha-toxin induced firm adhesion of the cells to fibrinogen and fibronectin. Incubation of rabbit neutrophils and neutrophil lysates with alpha-toxin led to the production of diacylglycerol (DG) and L-alpha-phosphatidic acid (PA), respectively. The toxin-induced DG and PA formation preceded the toxin-induced adhesion of the neutrophils to fibrinogen and fibronectin, and the production of O(2)(-). Pertussis toxin inhibited the alpha-toxin-induced formation of PA, the adhesion of the neutrophils to fibrinogen and production. GTP gamma S stimulated the events induced by the alpha-toxin, whereas GDP beta S inhibited them. The alpha-toxin stimulated phosphorylation of a protein with a molecular mass of about 40 kDa. In addition, treatment of the cells with 1-oleoyl-2-acetyl-sn-glycerol (OAG) and phorbol-12,13-dibutyrate (PDBu) stimulated cell adhesion, production of and phosphorylation of the 40 kDa protein, but had no effect on the formation of PA. The events induced by the presence of OAG and PDBu were not inhibited by pertussis toxin. Protein kinase C inhibitors, H-7, staurosporine and chelerythrine, blocked alpha-toxin-induced adhesion, production of O(2)(-)and phosphorylation of the 40 kDa protein. These observations suggested that alpha-toxin-stimulated adhesion to the matrix and production were due to the formation of DG, through activation of phospholipid metabolism by a pertussis-toxin-sensitive GTP-binding protein, followed by activation of protein kinase C by DG.

Production of phospholipase C (alpha-toxin), haemolysins and lethal toxins by Clostridium perfringens types A to D

To obtain high yields of extracellular enzymes and toxins for immunological analysis, type culture collection strains of Clostridium perfringens types A to D and 28 fresh isolates of C. perfringens type A from humans were grown in fermenters under controlled conditions in a pre-reduced proteose peptone medium. The type culture collection strains all showed different characteristics with respect to growth rates and pH optima for growth. Production of phospholipase C (alpha-toxin), haemolysin and lethal activity varied considerably between the different types. Growth and extracellular protein production in fermenters with pH control and static or stirred cultures were compared. Production of all extracellular proteins measured was markedly improved by cultivation in fermenters with pH control. Strain ATCC13124 produced five times more phospholipase C than any of 28 freshly isolated strains of C. perfringens type A, grown under identical conditions. Haemolytic and lethal activities of the ATCC strain were equal or superior to the activities of any of the freshly isolated strains. There were no differences in the bacterial yields and in the production of extracellular toxins between type A strains isolated from clinical cases of gas gangrene and abdominal wounds, and those isolated from faecal samples from healthy persons.

Necrotizing infections of subcutaneous tissue and fascia

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