Clostridium perfringens: morphology, cultural characteristics, classification and laboratory diagnosis
Clostridium perfringens (Clostridium welchii) is a normal inhabitant of large intestine of human and animal and found in feces and skin of perineum, buttocks and thigh. Spores are commonly found in soil, dust and air.
It is a rectangular gram positive bacillus with rounded or truncated ends usually occurring in singles, chains or small bundles. It is capsulated and non motile. Spores are central or subterminal but are rarely seen.
It is an anaerobe but can grow under microaerophilic condition. Oxygen is not actively toxic and cultures do not die on exposure to air. It can grow over a pH range of 5.5- 8 and temperature range of 20oC -50oC (optimal being 45oC). There is good growth of this organism on Robertson’s cooked meat medium in which meat is turned pink and not digested. It forms irregular, spreading colonies on blood agar surrounded by a double zone of haemolysis known as target haemolysis (i.e. inner narrow zone of complete lysis due to θ-toxin and wider outer zone of partial haemolysis due to α-toxin).
Classification of Clostridium perfringens
Strains of C. perfringens are classified as 5 biotypes A – E depending on the differential production of four major lethal toxins (alpha, beta, epsilon and iota). In addition, strains of C. perfringens may also produce a number of other toxins, including: neuraminidase and enterotoxin
Skin and Soft tissue: gas gangrene, cellulitis
Gastrointestinal: necrotising enteritis, food poisoning;
Gynaecological: septic abortion
Gram stained smears and culture of clinical samples e.g. blood, pus and tissue may provide evidence of clostridial infection. Recovery of C. perfringens on simple or selective agar provides a definitive diagnosis. Identification of C. perfringens can be determined through biochemical tests (e.g. API 20A, Rapid ID 32A kits). Confirmation of a-toxin and lipase production can be established on egg-yolk agar (Nagler plate); toxin-producing strains generate a zone of opalescence around the colonies, which can be inhibited by specific antitoxin to α-toxin.
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