Clostridium botulinum Part 1; Biochemical Properties, types of botulism and production of toxin

This is the 1st video on the Clostridium botulinum and is focusing the biochemical properties, types of botulism, and production of toxins.
Clostridium botulinum is a bacterium that is ubiquitously found in the soil and cause Botulism. The endospores of C. botulinum are sub-terminally placed or located on the bacterium and they are oval in shape. C. botulinum is found in the genus Clostridium and class Clostridia; and members are known to cause food spoilage, gas gangrene, botulism, and tetanus. Clostridium species are able to ferment a wide variety of organic compounds, and they produce butyric acid, acetic acid, butanol and acetone, and large amounts of gas (CO2 and H2) as of end products during the fermentation of sugars. The ability of Clostridium species to produce gas under anaerobic conditions is the reason why most canned foods contaminated by the pathogen are swollen. It is the causative agent of botulism, non-communicable disease, and a type of food poisoning caused by the exotoxin produced by C. botulinum.
It produces dangerous toxins (botulinum toxins) under low-oxygen conditions. Botulinum toxins are one of the most lethal substances known which block nerve functions and can lead to respiratory and muscular paralysis. Homemade canned, preserved, or fermented foodstuffs are a common source of foodborne botulism and their preparation requires extra caution.
Biochemical Properties/ Laboratory Identification
Clostridium botulinum is rod-shaped (Bacilli), Gram-positive, motile, Endospore forming, Anaerobic, and Catalase negative bacteria.
Pathogenesis of Clostridium botulinum Infection
C. botulinum is a diverse group of pathogenic bacteria grouped together by their ability to produce botulinum toxin (neurotoxin). C. botulinum is responsible for
a. Foodborne botulism (ingestion of preformed toxin),
b. Infant botulism (intestinal infection with toxin-forming C. botulinum)
c. wound botulism (infection of a wound with C. botulinum).
C. botulinum produces heat-resistant endospores that are commonly found in soil and are able to survive under adverse conditions. C. botulinum is only able to produce the neurotoxin during sporulation [formation of spores from vegetative cells during unfavorable environmental conditions], which can only happen in an anaerobic environment.
• This anaerobic environment is provided by cans and bulging canned food; bulging, misshapen cans are due to an internal increase in pressure caused by gas produced by the bacteria.
• This is among the most toxic and potent neurotoxin known to humankind, natural or synthetic, with a lethal dose of 1.3–2.1ng/kg in humans i.e. even microscopic amounts can cause illness or death.
• C. botulinum produces eight different types of neurotoxins designated by the letters A through H; only types A, B, E, F, and H cause illness in humans. Types A, B, and E are associated with food-borne illness, with type E specifically associated with fish products.
• Type C produces limber-neck in birds and type D causes botulism in other mammals. No disease is associated with type G.
• The "gold standard" for determining toxin type is a mouse bioassay, but the genes for types A, B, E, and F can now be readily differentiated using quantitative PCR.
• As no antitoxin to type H is yet available, discovered in 2013, and is thus by far the deadliest. They are resistant to degradation by enzymes found in the gastrointestinal tract. This allows for ingested toxins to be absorbed from the intestines into the bloodstream. However, all types of botulinum toxin are rapidly destroyed by heating to 100°C for 15 minutes (900 seconds).
How is the Toxin Produced in Food?
C. botulinum spores are often found on the surfaces of fruits and vegetables and in seafood. The organism grows best under low-oxygen conditions and produces spores and toxins. The toxin is most commonly formed when food is improperly processed (canned) at home. C. botulinum cannot grow below a pH of 4.6, so acidic foods, such as most fruits, tomatoes, and pickles, can be safely processed in a water bath canner. However, foods with a higher pH (most vegetables and meats) must be processed under pressure. Therefore, a pressure cooker should be used. The pressure cooker will reach high enough temperatures to destroy the C. botulinum spores.
For example, if a low-acid food, such as green beans, is canned improperly (not canned under pressure or improperly canned using a pressure canner), C. botulinum bacteria will be destroyed by the boiling of water and food, but the C. botulinum spores will not be destroyed. The canning process will remove the oxygen from the jar, creating a low-oxygen environment that is will allow the spores to produce the toxin. However, the toxin is sensitive to heat and can be destroyed if the food in question is boiled for 10 minutes before use (longer at high altitudes).

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