It is the causative agent of botulism.
It is a non-capsulated, Gram-positive bacillus. It is motile by peritrichous flagella and bears oval, bulging, subterminal spores.
Cl. botulinum is classified based on the antigenicity of botulinum toxin into seven types: A to G.
Pathogenicity is due to botulinum toxin. This neurotoxin is a protease that cleaves proteins involved in the release of acetylcholine at neural synapses and the neuromuscular junction. As a result, acetylcholine can’t be released, leading to flaccid paralysis.
Three types of botulism are seen: food-borne, wound, and infant botulism.
Food-borne botulism: Food can be contaminated with Cl. botulinum spores, which germinate under anaerobic conditions and produce a potent neurotoxin. It is commonly associated with improperly canned meat and meat products, and alkaline foods such as beans, mushrooms, peppers, etc.
The first symptoms of botulism are nausea, vomiting, weakness, and vertigo (dizziness). These are followed by neurological symptoms: visual impairments (blurred or double vision), loss of normal throat and mouth functions (difficulty speaking and swallowing; dry mouth, throat, and tongue; and sore throat), general fatigue, lack of muscle coordination, and difficulty in breathing. Gastrointestinal symptoms may include abdominal pain, diarrhea, or constipation. Death is usually caused by respiratory failure and airway obstructions. Symptoms typically appear in 12-36 hours. It presents as a descending paralysis.
Infant botulism: This is associated with ingestion of honey contaminated with Cl. botulinum spores in infants, typically less than 2 months of age. Clinical features are similar to food-borne botulism.
Wound botulism: Wounds can be contaminated with spores, which then germinate locally and produce botulinum toxin that is absorbed into the body. Symptoms are similar to food-borne botulism, except for gastrointestinal symptoms. It is seen in drug abusers.
Prevention of botulism includes proper canning of food; discarding swollen, gassy, or spoiled canned foods; adding nitrates and nitrites to meat and meat products; refrigerating all food within 2 hours of cooking; boiling foods for at least 10 minutes; and avoiding feeding honey to infants.
Contaminated food and fecal matter can be used as specimens for diagnosis. Gram stain may show typical Gram-positive bacilli.
Culture is not always done. When performed, it is done under anaerobic conditions on blood agar, nutrient agar, Robertson’s cooked medium (RCM) (where it causes blackening of meat particles and gas production), and lactose egg yolk milk agar medium (where it produces opalescence and a pearly layer).
Diagnosis is mainly clinical and is supported by demonstrating toxin in clinical samples by intraperitoneal inoculation into mice or guinea pigs. The test animal dies if toxin is present in the sample, while control animals given antitoxin will survive.