SMLS LECTURE SERIES GENUS: CLOSTRIDIUM

s General Characteristics Members of the genus Clostridium are fat and short or pleomorphic, spore-forming anaerobic Gram positive rods. Type species: C. perfringens. Other very important species are C. tetani, C. botulinum and C. difficile.

Habitat: Found in soil, water, sewage and some form part of the normal flora of GIT of man and animals. Toxins: Medically important species produce toxins some of which are very lethal. Antibiotic sensitivity: The species are usually sensitive to penicillin, metronidazole, clindamycin and erythromicin but are all resistant to gentamicin.

C. perfringens: Morphology: A short and fat bacillus which does not readily produce spores. It may exhibit pleomorphism. Culture: Grows well on BA anaerobically at 370C. Selectively isolated with gentamicin blood agar. Some strains are beta haemolytic and show double haemolysis on BA.

Typing: Five types of C. perfringens A, B, C, D and E, based on the 12 toxins produced. Type A is the only human pathogen. Toxins: All types produce alpha toxin

The toxin, also known as phospholipase C enzyme, or lecithinase, causes the breakdown of lecithin in mammalian cell membrane. Basis for “Nagler” reaction. Other toxins: several other toxins are produced by the various types. Identification: Based on the neutralisation of alpha toxin with specific antitoxin. This is known as Nagler reaction.

Pathogenicity: Causes: - Gas gangrene: wounds associated with overwhelming destruction of tissue. - Food poisoning: when ingested in large numbers, produce entero toxin resulting in diarrhoea. C. tetani Morphology: Longer than C. perfringens but with distinctive terminal spores – “drumstick” appearance.

Toxin A highly potent toxin which is a protein Toxin A highly potent toxin which is a protein. Two types: - Tetanospasmin: A neurotoxin responsible for the clinical manifestation of tetanus. It blocks the release of neurotransmitters for inhibitory snapses thus causing excitatory snaptic activity to be unregulated. ,

-Tetanolysin: An oxygen labile toxin whose clinical significance is not fully understood. Pathogenicity: Tetanus results from contamination of wound by the organism resulting in the release of toxin. Tetanus may result from puncture wounds, septic abortion, circumscion or ear-piercing as result of using unsterile instruments.

Culture: Grows well on BA; strict anaerobe, beta haemolytic Culture: Grows well on BA; strict anaerobe, beta haemolytic. Prevention and control: ATS vaccine. C. botulinum Found in soil, water, vegetable etc Seven types are recognised: Types A, B, C, D, E, F, and G.

Pathogenicity: Types A, B, E and F cause severe and usually fatal form of food poisoning, botulism in human. The toxin is the most active known poison. Infection is by ingestion of the pre-formed toxin in preserved food, usually home canned meat, and fish products. Signs and symptoms: Within 12 – 26 hours of ingestion, vomiting, thirst, constipation, blurred vision,

difficulty in swallowing, speaking and breathing difficulty in swallowing, speaking and breathing. Death occurs 1 – 5 days after on set. Type C causes limber-neck in fowls. Type D causes botulism in cattle. Culture: Strict anaerobe, grows well on BA with beta haemolysis. Identification: Toxin neutralisation with specific anti toxin.

C. difficile Found as commensals in the GIT of 3-5% of healthy persons C. difficile Found as commensals in the GIT of 3-5% of healthy persons. Pathogenicity: causes pseudomembraneous colitis following the use of broad spectrum antibiotics. The antibiotics eliminate other normal flora of the gut, thus allowing C.difficile to overgrow and produce its entero toxin.

Culture : Isolation from faeces on an aerobic selective medium Culture : Isolation from faeces on an aerobic selective medium. Identification: Colonies fluoresce under UV light as well as carbohydrate fermentation. Toxin: Toxin detection method is available. Refer to specialist text books for details!