Gas gangrene causative agents

Etiology and main pathogens

The disease is caused by Gram-positive spore-forming bacilli of the genus Clostridium. Four species play a leading role in the etiology:

• C. perfringens is the primary pathogen, accounting for up to 80% of all cases.
• C. novyi (formerly C. oedematiens) causes 20–30% of cases.
• C. septicum is detected in 10–15% of episodes.
• C. histolyticum is found in 5–10% of patients.

The source of infection is soil and the intestinal tract of humans or animals, and transmission occurs via contact when soil enters a wound.

Morphology and cultural characteristics

Gas gangrene clostridia are large bacilli. Most species are motile and non-capsulated, whereas C. perfringens is non-motile and surrounded by a protective capsule. Bacterial spores are oval or spherical, exceeding the cell diameter and giving it a spindle or club shape.

By type of respiration, the microorganisms are obligate anaerobes. Special physical, chemical, and biological methods of creating an oxygen-free environment are used for their cultivation. In liquid media (e.g., thioglycollate broth or Robertson's cooked meat medium), vigorous turbidity and gas production are observed.

Pathogenicity factors and toxins

The pathogenic effect of C. perfringens is due to a complex array of exotoxins and enzymes:

1. α-toxin (lecithinase C): possesses lethal, hemolytic, and dermonecrotic activity.
2. κ- and λ-toxins: collagenases and proteinases that destroy connective tissue and muscles.
3. Spreading factors: increase tissue permeability and promote deep penetration of the infection.

The action of toxins leads to enzymatic hydrolysis of cell membranes, massive edema, and tissue autolysis.

Clinical presentation and diagnostics

The incubation period of the wound infection lasts 1–3 days. The disease begins with severe pain in the wound and rapidly progressing "cold" edema. At the height of the disease, characteristic crepitus (crunching upon palpation due to gas accumulation) appears, the exudate acquires a putrid odor, and the muscles resemble "boiled meat".

To confirm the diagnosis, the following are used:

• Bacterioscopy: detection of large Gram-positive encapsulated bacilli.
• Bacteriological method: inoculation onto enrichment media.
• Toxin indication: bioassay and neutralization test in laboratory animals.

Class and exam questions

What else to study on this topic

• Historical background and description of anaerobic infection by Ambroise Paré and N.I. Pirogov
• Classification of Clostridium perfringens serovars (A to F) and their toxin production
• Methods for creating anaerobic conditions in laboratory practice
• Specific differential media (Wilson–Blair medium, litmus milk)
• Foodborne toxicoinfections caused by Clostridium perfringens

Other topics in the section "Gram-positive spore-forming bacilli (Anthrax, Clostridia: tetanus, botulism, gas gangrene, difficile)"

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