Radiation Resistance of Spores of Type E Clostridium As Related to Extension of the Refrigerated Storage Life of Foods^a,b

Abstract

Spores of three strains of Clostridium botulinurn Type E were inoculated into 202 x 202 cans of beef stew and irradiated to permit the survival of a small number of spores per container. The cans containing survivors were incubated at 43 and 49°F to determine whether germination and outgrowth of surviving spores could take place. With all three strains at least some of the survivors were capable of developing to the point of producing swell spoilage and toxin at both temperatures.The significance. of these results in relation to extension of the refrigerated storage' life of food by radiation "pasteurization" is discussed.

Growth and Toxin Production by Type E Clostridium Botulinum Below 40°Fa

“…It is our hope that these results will stimulate considerable additional investigation in this field in the near future. Schmidt et al (1961a), in an experiment preliminary to determining the ability of spores surviving irradiation to germinate and result in outgrowth at refrigeration temperatures, tested the ability of miIdly heatshocked spores to germinate and develop in beef stew at 43 and 49°F. Approximately the same inoculum level of spores and procedure were used as in this work with strains VII, Iwanai, and Beluga.…”

“…However, since this work was done before recognition of the potentiation of Type E toxin by trypsin (Duff et al 1956), the complete absence of toxin in any of these cultures is uncertain. Schmidt et al (1961a) reported that small numbers of Type E spores permitted to survive radiation pasteurization doses were able 'Presented at the 21st Annual Meeting of the Institute of Food Technologists, May 8, 1961. to germinate and produce toxic outgrowth at 43 and 49°F during comparatively short periods of storage. Strains VH, Beluga, and Iwanai were used in that work, and it was also shown that mildly heat-shocked spore inocula germinated and produced toxic outgrowth at those temperatures.…”

“…However, it must be pointed out that those experiments consisted of duplicate tubes each inoculated with 10,000 spores of the strain being studied. Schmidt et al (1961a) also suggested that the implications of the various results obtained to date make it desirable that an intensive study be conducted to determine the absolute minimum temperature that permits outgrowth of Type E spores using high-spore-level inocula. This paper pre-sents the results of studies that attempt in a preliminary way to determine the ability for outgrowth, at 34, 36, and 38°F of heatshocked spores of 4 strains of Cl.…”

“…Strains VH, Beluga, and Iwanai were used in that work, and it was also shown that mildly heat-shocked spore inocula germinated and produced toxic outgrowth at those temperatures. Schmidt et al (1961a) discussed. the results of experiments from 3 different laboratories in relation to the extension of the refrigerated storage life of food products by radiation pasteurization.…”

Biophysical Aspects of Clostridia

“…Although no systematic study had been undertaken, it soon became apparent that in contrast to Cl. botulinum types A and B, the relatively heat sensitive strains of type E and F appeared also to be sensitive to ionizing radiations (Schmidt, Lechowich & Nank, 1962;Anellis, Grecz & Berkowitz, unpublished). Furthermore, it was interesting to find that the highly heat resistant spores of PA 3679 (Townsend, Esty & Baselt, 1938) as well as those of Cl.…”