Botulism:
- Botulism is a neuro paralytic intoxication caused by ingestion of preformed enterotoxin in food produced by Clostridium botulinum.
- Etiological agent for Botulism:
- Clostridium botulinum is gram +ve, anaerobic, rod shaped, spore forming bacteria.
- They produce 8-types of neurotoxins (A, B, C1, C2, D, E, F and G) in food.
- Therefore, Clostridium botulinum strains are classified into 8-group on the basis of type of neurotoxin they produce.
- Type A, B, E and F cause botulism in human being and type C and D cause botulism in other animals.
- It usually produces gas in food. It may or may not be proteolytic.
- Proteolytic strain produces various bad smelling compounds like H2S in food.
- But, in case of non-proteolytic strain, spoilage cannot be judged by smell of food.
- Similarly, bad odor is not developed in low protein or non-protein food.
- Various factors affect spore germination growth and toxin production by C. botulinum.
- Moisture below 30% inhibit toxin production. Similarly, salt concentration of 8% or more prevent neurotoxin production in food.
- Similarly, neurotoxin is not produced if pH of food is 4.5 or below.
- Composition of food determine type of toxin produced. For.eg. food containing milk or casein give more toxic type of type A toxin.
Properties of botulinum toxin (Botox):
- Toxin is produced in food during growth and autolysis of bacteria.
- Proteolytic strain produce toxin in active form but some non-proteolytic strain produce toxin in inactive form.
- This inactive toxin become active in stomach by acid hydrolysis.
- Unlike enterotoxin of S. aureus, this neurotoxin is damaged by heating at 80oC for 10 minutes.
- Botulinum toxin is most toxic chemical found in nature.
Pathogenesis of botulism:
- Botulism occur by ingestion of pre-formed neurotoxin on food.
- After ingestion it is absorbed by cell of upper intestinal tract, then enters into lymph then into blood.
- From blood, it reaches neuromuscular junction and binds to nerve ending. After binding it inhibit release of acetylcholine neurotransmitter that gives paralysis of muscle.
- If this paralysis extends to breathing muscle, death occurs by respiratory failure.
Infant botulism:
- In adult botulism is intoxication i.e. it is caused by ingestion of preformed neurotoxin of Clostridium botulinum in food.
- In adult, ingested Clostridium botulinum cannot multiply in intestinal tract.
- It is because Clostridium botulinum is highly acid sensitive and it is killed by stomach acidity.
- Furthermore, this bacteria is very less competitive and cannot compete with normal flora of intestinal tract.
- So, in case of adult botulism occurs only by ingestion of pre-formed neurotoxin, but not by ingestion of bacterial cell but in infant stomach is not acidic and intestinal normal flora are not fully developed.
- Therefore, ingested Clostridium botulinum multiply and produce endotoxin in intestinal tract of infant.
- So, botulism in infant is an example of food infection.
Symptoms of Botulism:
- Incubation period is 12-36hrs, but it may be shorter or longer.
- Earliest symptom includes acute digestive disturbance followed by vomiting, sometime diarrhea, fatigue and headache.
- After above symptoms typical neurological symptoms appear. They include double vision, difficulty in speaking and swallowing, mouth becomes dry and tongue swells.
- Paralysis of involuntary muscle occurs. Paralysis of respiratory muscle results in death.
Treatment of Botulism:
- Treatment of botulism can be separated into three processes:
- First treatment is removal of unabsorbed neurotoxin from intestinal tract. For.eg. by inducing vomiting.
- Second treatment involves neutralization of neurotoxin by ingestion of antibody (anti-toxin). It is the only one successful treatment of botulism.
- Third treatment involves curing of symptoms. For.eg. by artificial breathing.
Prevention and control of botulism:
- Preventing contamination of food:
- For this purpose, food should be kept away from soil and dust because its natural habitat is soil.
- Preventing growth and toxin production in food:
- It can be done by making the food aerobic by adding chemicals, heat treatment etc.
- Damaging neurotoxin in food:
- It can be done by heating the food at 80oC for 10 minutes just before eating.