Fish Microbiology and Quality Assurance

Unit 5 - Foodborne pathogens

5.2. Clostridium botulinum food intoxication
Botulism is a food borne illness caused by the ingestion of food containing neurotoxin produced by Clostridium botulinum. It is a Gram positive rod shaped anaerobic spore forming soil bacterium which can grow in the pH range of 4.6 to 8.5. It produces highly potent exotoxin, a neurotoxin, and ingestion of a small quantity (few nanograms: 30-100 ng) can cause paralyses and death.

Toxin types
Seven neurological toxin types (Type A to G) have been recognized based on toxin specificity. Of these types A, B, E and F are pathogenic to man. These are further divided into 2 types.

• Proteolytic types: Includes A, B, and F type toxin producers. These are heat resistant, NaCl tolerant, mesophilic and soil is the general habitat.
• Non-proteolytic types: Includes some strains of B, E, and F. these are heat sensitive, psychrotolerant, NaCl sensitive and aquatic environment is the natural habitat.

Toxins produced by type A, B, E and F cause human botulism. Botulinal toxin is one of the most potent of all poisons and very low amounts (30 -100 ng) can cause death.

Clostridium botulinum Type E
C.Botulinum Type E is associated with fish and fishery products and is primarily of marine origin. It is ubiquitous in natural environment including marine sediment as well as animals, birds and fish intestine. Toxin production by Cl. botulinum depends on the ability of cells to grow in food and autolyse to release toxins.

Factors influencing toxin production

• Toxin production depends on the factors influencing spore germination and growth. These include composition of food, moisture current, pH, O-R potential, salt content and temperature and storage conditions.
• In heat processed foods C.botulinum are of great significance, as under-serilization can lead to survival of spore, which under suitable conditions germinate and make food toxic. Even seafood held at low temperature (refrigerated temperature) the type E can grow (at about 3^oC). But fail to grow under frozen temperature.
• For the intoxication to develop the preformed toxins should be consumed (food containing toxin). Food that has been eaten which was served without heating prior to serving can cause illness. The toxin is inactivated when heated at 60^oC for 5 min. Botulism occurs rarely (incidence of botulism is not common) and most of the outbreaks are associated with fish (Type E).

Symptoms of food poisoning
Symptoms vary from mild illness to fatal condition within 24 hr, symptoms develop within 12-36 hr and include nausea and vomiting followed by neurological disorders like visual impairment, loss of normal function of mouth and throat, lack of muscle coordination, respiratory impairment leading the death. Onset of symptoms is rapid with type E botulism, while the severity is high with type A

Treatment
Only known method of treatment is by administration of antitoxin and is effective only when administered before onset of symptoms.

Conditions necessary for outbreaks

• Presence of spores of type A, B, E or F in food being canned or processed.
• Food in which the spores can germinate and clostridia can grow and produce toxin.
• Survival of spores because of inadequate heating in canning or inadequate processing.
• Condition (environmental/storage) after processing that will permit germination of spores.
• Insufficient cooking of food to inactive the toxin.
• Ingestion of toxin bearing food.

Prevention of outbreaks

• Use of approved heat process for canned foods.
• Rejection of all swollen or spoiled canned foods.
• Refusal even to taste a doubtful food.
• Avoidance of foods that have been cooked held but not well heated.
• Boiling of suspected food for atleast 15 min to inactive toxin.