gram-positive rods, the obligate anaerobic

Clostridia are large gram-positive rods, the obligate anaerobic, blunt-ended rods. They form endospores; the position of the developing spore within the vegetative cell is useful in identifying the species. Most species are motile. These organisms also synthesize some of the most potent exotoxins. Clinically significant species of Clostridium include C. perfringens, which causes (gas gangrene) and food poisoning; C. difficile, which causes pseudomembranous colitis associated with antibiotic use; C. tetani, which causes tetanus and C. botulinum, which causes botulism.
A. Clostridium perfringens
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. C. perfringens can cause anaerobic cellulitis, and myonecrosis (gas gangrene). Some strains cause a common form of food poisoning.
Pathogenesis:
C. perfringens secretes a variety of exotoxins, enterotoxins, and hydrolytic enzymes that facilitate the disease process.
1. Exotoxins: C. perfringens elaborates at least 12 exotoxins. The most important of these required for virulence in tissue, is alpha toxin. Alpha toxin is a lecithinase that degrades lecithin in mammalian cell membranes, causing lysis of endothelial cells, as well as RBC, WBC and platelets.
2. Enterotoxin: a small protein, acts in the lower portion of the small intestine, and causes loss of fluid and intracellular proteins.
3. Degradative enzymes: it is produces of hydrolytic enzymes, including proteases, DNases, hyaluronidase, and collagenases, which liquefy tissue and promote the spread of infection.