BOTULISM AND HOME CANNING 15 



PROPERTIES OF THE TOXIN PRODUCED BY 

 CLOSTRIDIUM BOTULINUM 



The toxin formed by CI. botulinum is a true exotoxin; that is, it is excreted 

 from the bacterial cell into the food where it remains unharmed for long periods. 

 This potent toxin appears to be produced whenever abundant growth occurs, 

 irrespective of the presence of fermentable carbohydrates. Jordan (1931) has 

 described botulism toxin as follows: 



Botulism toxin differs from any other known bacterial toxin in that it 

 N is not destroyed by the gastric-intestinal secretions. It is extremely 

 potent when tested either orally or parenterally, a culture filtrate sub- 

 cutaneously injected frequently kills guinea pigs in a dose of 0.0001 cc; 

 when the filtrate is fed to guinea pigs 0.001 cc. often prove fatal. Briegen 

 and Kempner obtained a toxin of which 0.000,001 cc. would kill a 250 gram 

 guinea pig. CI. botulinum may be likened to certain of the higher plants, 

 such as poisonous mushrooms, the deadly night shade, and the fungus of 

 ergot, which are dangerous by virtue of the poisonous compounds that 

 are generated in their cells or in the substances which they proliferate. 



Effect of Freezing 



James (1933) has reported experiments in which botulinum toxin was frozen 

 and defrosted 15 times without any reduction in strength. It would appear that 

 this toxin is not affected by continued or intermittent freezing. 



Effect of Heat 



The toxin of CI. botulinum is readily destroyed by heat. Thorn (1922) pointed 

 out that the *-emperature required to destroy this toxin varies considerably with 

 the strain of the organism that is used, but that in every experiment' reported, 

 all trace of toxicity had disappeared in products actually heated throughout to 

 185°F. (85°C.), for a very few minutes. Tanner and Twohe}' (1926) concluded 

 that (1) Under the conditions of the experiment the detoxification of the canned 

 foods containing CI. botulinum toxin required from 4 to 20 minutes heating at 

 212°F. (100°C.), (boiling water); from 25 to 45 minutes at 194°F. (90°C.); from 

 25 to 80 minutes at 176°F. (80°C.); from 45 to 75 minutes at 158°F. (70°C.); 

 and longer than 43^ hours at 140°F. (60°C.). (2) The variation in the time re- 

 quired to destroy the toxin was explained on the basis of heat penetration into 

 the product and variation in toxin content. Probably the same factors determine 

 the destruction of toxin in canned foods that explain the destruction of bacteria 

 during the canning process. (3) Heating of toxic foods to boiling under the usual 

 conditions may not render them free from toxin. Suspicious foods, whether 

 preserved bj- canning or other procedures, should not be eaten. 



In 1943 the United States Department of Agriculture (1943) made the follow- 

 ing recommendation for destroying botulinum toxin that might be present in 

 home-canned foods. 



Home-canned non-acid vegetables processed by the boiling water bath 

 method can contain botulinum toxin even if there are no signs of spoilage. 

 To be safe, such products should be brought to a boil and boiled for at 

 least ten minutes after the can or jar is emptied before they are eaten or 

 even tasted. Boiling for a full ten minutes or more will destroy the toxin, 

 though not the botulinum spores. It is the toxin, not the organism itself, 

 that is harmful. 



