C. perfringens is a large, nonmotile, gram-positive, encapsulated bacillus. It is ubiquitous in nature, with its vegetative form as part of the normal flora of the vagina and gastrointestinal (GI) tract. Its spores are found in soil. [Note: Spores are rarely seen in the body or following in vitro cultivation.] When introduced into tissue, however, C. perfringens can cause anaerobic cellulitis and myonecrosis (gas gangrene). Some strains of C. perfringens also cause a common form of food poisoning.

1. Pathogenesis: C. perfringens secretes a variety of exotoxins, enterotoxins, and hydrolytic enzymes that facilitate the disease process (Figure 1).

Fig1. Toxins and degradative enzymes produced by Clostridium perfringens. ET = enterotoxin.

a. Exotoxins: C. perfringens elaborates at least 12 exotoxins, designated by Greek letters. The most important of these, and the one that seems to be required for virulence in tissue, is α toxin. α Toxin is a lecithinase (phospholipase C) that degrades lecithin in mammalian cell membranes, causing lysis of endothelial cells as well as erythrocytes, leukocytes, and platelets. Other C. perfringens exotoxins have hemolytic or other cytotoxic and necrotic effects, either locally or when dispersed in the bloodstream. Perfringolysin O, or theta (θ) toxin, is a cholesterol-dependent hemolysin and an important virulence factor. C. perfringens strains are grouped A through E on the basis of their spectrum of exotoxins. Type A strains, which produce both α toxin and enterotoxin, are responsible for most human clostridial infections.

b. Enterotoxin: C. perfringens enterotoxin, a small, heat-labile protein, acts in the lower portion of the small intestine. The molecule binds to receptors on the epithelial cell surface and alters the cell membrane, disrupting ion transport (primarily in the ileum) and leading to loss of fluid and intracellular proteins. Interestingly, enterotoxin-producing strains are unusually heat resistant, the spores remaining viable for longer than an hour at 100oC, enhancing their threat as foodborne pathogens.

 c. Degradative enzymes: C. perfringens is a metabolically vigorous organism that produces a variety of hydrolytic enzymes, including proteases, DNases, hyaluronidase, and collagenases, which liquefy tissue and promote the spread of infection. The resulting degradation products serve as fermentation substrates for the rapid metabolism of C. perfringens. This organism has one of the fastest doubling times recorded, at less than 10 minutes.

2. Clinical significance: The disease processes initiated by C. perfringens result from a combination of infection and the production of exotoxins and/or enterotoxins and degradative enzymes.

a. Myonecrosis (gas gangrene): Clostridial spores are introduced into tissue, for example, by contamination with infected soil, or by endogenous transfer from the intestinal tract. Severe and open wounds, such as compound fractures and other ischemia producing injuries (for example, crush injuries), are a prime pre disposing condition. α Toxin and other exotoxins are secreted, and extensive cell death ensues. Production of enzymes that breakdown extracellular matrix facilitates the spread of infection. Fermentation of tissue carbohydrates, lipids, and amino acids yields gas, and an accumulation of gas bubbles in the subcutaneous spaces produces a crinkling sensation on palpation (crepitation), hence, the name “gas gangrene” (Figure 1). [Note: The rapidly accumulating gas itself is a virulence factor because it dissects along tissue planes. By enlarging these potential spaces, the clostridia progress much more rapidly due to the decreased resistance they create with gas.] The majority of infections resulting in necrosis of muscle are due to Clostridium species (gas gangrene) and group A streptococci. The exudates are copious and foul smelling. As the dis ease progresses, increased capillary permeability allows exotoxins to be carried from damaged tissue to other organs, resulting in systemic effects, such as shock, renal failure, and intravascular hemolysis. Untreated clostridial myonecrosis is uniformly fatal within days of the initiation of gangrene.

Fig2. Gas gangrene of arm.

b. Anaerobic cellulitis: This is a clostridial infection of connective tissue in which the spread of bacterial growth along fascial planes (fasciitis) does not involve invasion of muscle tissue. Necrotizing processes play a more limited role, but surgical intervention is generally unsuccessful (unless it is carried out very promptly and aggressively) because of the rapid spread of infection and compromise of blood supply due to swelling beneath tight fascia.

 c. Foodborne infection: C. perfringens is a common cause of foodborne infection in the United States. Typically, the onset of nausea, abdominal cramps, and diarrhea occurs 8 to 18 hours after eating contaminated food. Fever is absent and vomiting rare. The attack is usually self-limited, with recovery within 1 to 2 days. The occurrence of clinical symptoms requires a large inoculum of 108 organisms or greater. Therefore, a typical episode of clostridial enterotoxin food poisoning involves cooking that fails to inactivate spores, followed by holding the food for several hours under conditions that allow bacterial germination and several cycles of growth. Vegetative cells are consumed in the contaminated product, and C. perfringens then reproduces following ingestion (food infection) and produces toxin in vivo. Meats, meat products, and gravy are the most commonly implicated foods in C. perfringens foodborne illness.

 d. Necrotic enteritis: Outbreaks of a necrotizing bowel disease with high mortality (greater than 50 percent) caused by C. perfringens have been sporadically reported. e. Clostridial endometritis: This condition is a grave complication of incomplete abortion or the use of inadequately sterilized instruments. Gangrenous infection of uterine tissue is followed by illness due to toxins and bacteremia.

3. Laboratory identification: Diagnosis of clostridial myonecrosis or cellulitis rests largely on clinical presentation. The presence of clostridia in clinical materials may be adventitious (that is, an accidental contamination). With Gram stain, however, specimens from diseased tissue usually show vegetative clostridial forms (large, gram-positive rods), accompanied by other bacteria and cellular debris. When cultured anaerobically on blood agar, C. perfringens grows rapidly, producing colonies with a unique double zone of hemolysis due to production of α toxin (partial hemolysis) and perfringolysin O (complete hemolysis) as shown in Figure 3. In food infection, the organism can be sought in suspected food and the patient's feces. Gram stain and other laboratory findings greatly help planning of antibiotic therapy in patients with clinical manifestations of gas gangrene.

Fig3. Clostridium perfringens. A. Colonies on blood agar showing double zone of hemolysis. B. Photomicrograph of Gram stain.

4. Treatment and prevention: The key to both prevention and treatment of gas gangrene is immediate and thorough removal of foreign material and devitalized tissue and exposure of the wound to O2. Hyperbaric oxygen chambers increase the tissue O2 tension in the affected part and inhibit the pathologic process. If debridement is unable to control the progression of the gangrene, amputation, when anatomically possible, is mandatory in gangrene. Supplementary to this is the administration of antibiotics in high doses. C. perfringens is sensitive to penicillin and several common inhibitors of prokaryotic protein synthesis. Because clostridial infections usually involve a mixture of species, the use of broad-spectrum antibiotics is appropriate.

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