“Autosterilization” as a Problem in the Bacteriological Examination of Canned Foods

Abstract

During investigations in which large numbers of cans of food spoiled by thermophilic bacteria were opened, many cans with evidences of spoilage contained no living bacteria even though examination of stained films revealed the presence of many cells. This seemed to indicate that the microorganisms responsible for the spoilage had probably died out. To secure more information on this situation which has become known as “autosterilization”, the problem was attacked with canned corn and several spoilage bacteria including an active thermophilic spoilage organism, No. 1518, in both tin and large culture tubes.

Large culture tubes were half-filled with fresh canned corn, layered with paraffin and sterilized in the autoclave. The corn in the tubes was then inoculated with the spoilage organisms and divided into 4 sets. One set was incubated at 10° C.; the second at room temperature (20-37°C); the third at 37.6°C, and the fourth at S5°C. At intervals of 2 or 3 days a tube from each group was removed, plated for the number of viable organisms, and the pH determined. A relationship between the temperatures at which the tubes were held and the number of living organisms was apparent with all cultures of thermophilic bacteria used. At 55°C. a lethal H ion concentration was reached, much more quickly than at 37°C. The tubes which were held at 55°C. had an original pH of 6.8 and a bacterial count of 4,000,000 per gm. At the end of 15 days, the count was reduced to 100 per gm. with a pH of 4.8. Further incubation at the same temperature for 4 or more days killed all of the organisms with practically no change in pH. A similar experiment was carried out with No. 2 cans of corn.