Clostridium perfringens

Also called Cl. welchii. It causes gas gangrene and food poisoning.

Morphology

It is a Gram positive bacilli, capsulated, non motile, arranged singly, in chains or bundles, with bulging oval and subterminal spores. Remember that spores would not be seen in clinical specimens. Can you guess why is it so?

Classification

6 antigenic types A to F depending on the type of toxin produced and 80 serotypes depending on surface polysaccharide have been identified.

Human Pathology

Gas gangrene and food poisoning are the major diseases caused by Cl perfringens. Apart from that it also causes necrotizing enteritis, brain abscess, meningitis, panophthalmitis, septicaemia, cellulitis and gangrenous appendicitis.

Gas Gangrene: Also called myonecrosis or necrotizing fasciitis. It follows war injuries, traffic accidents etc where the wound gets contaminated with bacteria which then start growing under anaerobic conditions in the wound and produce toxins which cause further damage. The infection and necrosis thus spreads and causes a filthy smelling gas production.

Alpha toxin is the major toxin responsible for the infective process as it breaks down tissues (necrotizing) by damaging the cell membranes. Patient presents with a foul smelling, necrotic wound with edema and local pain, crepitations due to gas formation and in severe cases, hypotension and shock from toxemia. It is fatal if not treated at the right time.

Food Poisoning: Food gets contaminated with heat resistant spores of Cl. perfringens. When such food especially meat dishes are reheated the bacteria grow exponentially and produce enterotoxin. The enterotoxin of Cl. perfringens is a superantigen and it acts on the small intestines to cause abdominal cramps and watery diarrhoea after an 8-16 hour incubation period.

Laboratory diagnosis of Cl.perfringens infections

Gas Gangrene: Specimens are taken from the wound including exudates and necrosed tissue. Gram stain shows many Gram positive bacilli without spores with scanty inflammatory infiltrate as toxins from Cl.perfringens break down the neutrophils. Anaerobic culture is done on blood agar and RCM. It shows characteristic target hemolysis with a zone of complete hemolysis from theta toxin followed by a wider zone of incomplete hemolysis due to alpha toxin. In RCM broth it turns the meat particles pink (not black), as it has saccharolytic activity but no proteolytic activity.

Biochemical identification is done with the litmus milk test and Nagler reaction. The Litmus milk test shows change in color of litmus paper from blue to red due to stormy fermentation with disruption of casein clot due to gas production. In Nagler reaction when Cl.perfringens is inoculated on a medium containing egg yolk or serum, a zone of opacity is produced around the colonies due to lecithinase activity of alpha toxin.

Food Poisoning: It is mainly a clinical diagnosis. Fecal matter and contaminated food can be obtained for anaerobic culture followed by biochemical identification same as in gas gangrene samples.