Clostridium perfringens

Overview: Clostridium perfringens is a Gram-positive, spore-forming, heat-resistant, rod-shaped anaerobic bacterium, widely distributed in soil, marine sediment, decaying vegetation, and the intestinal tract of insects, humans and other vertebrates. C. perfringens is a member of the family Clostridiaceae of the Clostridiales, and is subdivided into five distanct serotypes, (A to E), on the basis of each isolate’s pattern of expression of four (alpha, beta, epsilon, and iota) of the 13 known C. perfringens toxins, which differ in their tropisms and toxigenicity. The virulence of C. perfringens derives largely from its prolific ability to express protein toxins and produce endospores. The spores produced by this organism persist in the environment and often contaminate raw food materials, causing a number of clinical conditions ranging from relatively mild food poisoning to the potentially life-threatening gas gangrene.

Figure 1. This photomicrograph reveals a numbers of Clostridium perfringens bacteria that had been grown in Schaedler’s broth, and subsequently stained using Gram-stain [1000 X].

Virulence and Pathogenicity: C. perfringens is linked to two types of food poisoning, namely, type A and type C. Type A is one of the most common human diseases caused by C. perfringens, which annually ranks among the leading foodborne diseases in industrialized countries. Type A induces a relatively minor gastrointestinal tract illness, causing diarrhea and abdominal cramps for roughly 24 hours following an 8 to 12 hour incubation period. C. perfringens enterotoxin (CPE) is the virulence factor responsible for symptoms associated with this illness, and the toxin is released when the mother cell lyses at the completion of sporulation in the gastrointestinal tract. CPE is a single 35 kDa (kiloDalton) polypeptide with a unique amino acid sequence and mechanism of action, and recent molecular epidemiology surveys suggest that only a 5% of all C. perfringens isolates carry the gene that encode this toxin, namely, the cpe gene (Czeczulin et al., 1996).

Type C food poisoning is a much more serious gastrointestinal tract disease, causing severe abdominal pain, dysentery (bloody diarrhea), and vomiting, following a five to six hour incubation period. After these initial symptoms, the person may experience necrotic inflammation of the small intestine. The disease is caused by the production of beta-toxin (β-haemolysin). Generally, human endothelial cells are sensitive to the toxic effect of beta-toxin, since it forms potential-dependent, cation-selective channels in lipid bilayers, inducing the release of arachidonic acid and leakage of inositol from these cells, in addition to the efflux of potassium ions and the influx of calcium, sodium, and chlorine ions.

Aside from food poisoning, infections due to C. perfringens can cause tissue necrosis, bacteremia, emphysematous cholecystitis, and gas gangrene, also known as clostridial myonecrosis. C. perfringens strains that produce alpha-toxin cause gas gangrene. Alpha-toxin possesses phospholipase C, sphingomyelinase, and biological activities that cause hemolysis, lethalitym, and dermonecrosis. The toxin is a zinc metallophospholipase that requires zinc for activation. First, the toxin binds to a binding site on the cell surface. The C-terminal domain of the protein toxin then bind a calcium ion, which allows the toxin to bind to the phospholipid head-groups on the cell surface. The C-terminal domain enters the phospholipid bilayer. The N-terminal domain has phospholipase activity. This property allows hydrolysis of phospholipids such as phosphatidyl choline, thus mimicking endogenous phospholipase C of the signal transduction pathway. The hydrolysis of phosphatidyl choline produces diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP₃) which activate a variety of second messenger pathways. The end result includes activation of arachidonic acid pathway and production of thromboxane A2, interleukin-8 (IL-8; involved in the inflammatory response, causing host damage), platelet-activating factor, and several intercellular adhesion molecules. These actions combine to cause edema due to increased vascular permeability.

C. perfringens strains that produce various gelatinolytic enzymes such as collagenase, a protease that cleaves native collagen in its triple helical conformation, also play a role in the physical attributes associated with gas gangrene (Matsushita et al., 1994). The structural breakdown of collagen - the framework of muscle protein - facilitates the formation gas gangrene. Consequently, the collagenase produced by this pathogen is involved in tissue necrosis, along with other toxins such as phospholipase C and thiol-activated haemolysin. Once the targetted cells have died due to infection, C. perfringens bacteria scavenge dead human cells for carbon producing gas as a byproduct of metabolism. In fact, C. perfringens bacteria produce a relatively large quantity of carbon dioxide, causing further tissue damage due to physical pressure.

Transmission: The bacteria can be found in soil and the feces of some people and animals. People can get sick by consuming food or water that may have come into contact with the bacteria, like food or water that has come into contact with animal feces or soil, undercooked meat and poultry, foods that have come into contact with dirty surfaces (unwashed cutting boards), cooked foods kept at room temperature for several hours, eating unwashed fruits and vegetables, or changing the diapers of infants infected with the bacteria, without proper handwashing.

Treatment: Surgical debridement, with amputation if necessary, is the mainstay of treatment for gas gangrene, while treatement for cases involving food poisoning are rarely administered. Antibiotics alone do not suffice by virtue of inadquete blood flow during tissue necrosis, but they should be given as an adjuvant to surgery. Gas gangrene can be treated with hyperbaric oxygen, which is toxic to the anaerobic C. perfringens. Susceptible patients should maintain careful foot care and should avoid trama.

References:

Czeczulin, J.R., Collie, R.E., & McClane, B.A. (1996). Regulated Expression of Clostridium perfringens Enterotoxin in Naturally cpe-Negative Type A, B, and C Isolates of C. perfringens. Infection and Immunity, 64(8): 3301–3309.

Matsushita, O., Yoshihara, K., et al. (1994). Purification and Characterization of a Clostridium perfringens 120-Kilodalton Collagenase and Nucleotide Sequence of the Corresponding Gene. Journal of Bacteriology, 176(1): 149-156.