Effect of Temperature of Liquid Nitrogen on Radiation Resistance of Spores of Clostridium botulinum1

Abstract

GRECZ, NICHOLAS (U.S. Army Natick Laboratories, Natick, Mass.), 0. P. SNYDER, A. A. WALKER, AND A. ANELLIS. Effect of temperature of liquid nitrogen on radiation resistance of spores of Clostridium botulinum. Appl. Microbiol. 13:527-536. 1965.-An apparatus consisting of a Dewar flask and a relay system controlling the flow of liquid nitrogen permitted the irradiation of samples in tin cans or Pyrex tubes at temperatures ranging from 0 i 1.5 C to -194 i 2 C. An inoculated pack comprising 320 cans of ground beef containing 5 X 104 spores of Clostridium botulinum 33A per can (10 cans per radiation dose) was irradiated with Co6O at 0 and -196 C. Incubation was carried out at 30 C for 6 months. Approximately 0.9 Mrad more radiation was required to inactivate the spores at -196 C than at 0 C. Cans irradiated at -196 C showed partial spoilage at 3.6 Mrad and no spoilage at 3.9 Mrad; the corresponding spoilage-no spoilage doses at 0 C were 2.7 and 3.0, respectively. The majority of positive cans swelled in 2 to 14 days; occasional swelling occurred as late as 20 days. At progressively higher doses, swelling was delayed proportionally to the radiation dose received. The remaining nonswollen cans had no toxin after 6 months of storage, although occasional cans contained very low numbers of viable spores comprising on the average 0.1% of the original spore inoculum.The Dio values in phosphate buffer were 0.290 Mrad for 0 C and 0.396 Mrad for -196 C; in ground beef, the corresponding D1o values were 0.463 Mrad and 0.680 Mrad, respectively. These D,o values indicate that the lethal effect of y rays decreased at -196 C as compared with 0 C by 13.5% in phosphate buffer, and by 47% in ground beef.1.5% agar.These two techniques, i.e., the spoilage endpoint, and the direct count technique, were also used for evaluation of spore survival in ground beef. With the end-point technique in glass tubes, the indications of viability of C. botulinum were turbidity, odor, and specific toxin; with canned beef, swelling of cans and specific toxin were the indicators. 527 on July 5, 2020 by guest http://aem.asm.org/ Downloaded from

Effects of Gamma Irradiation at ‐78°C on Microbial Populations in Dairy Products

“…The values in our study compared favorably to a study by Anellis et al (1975), indicating that at -3o"C, a 12D of 43 kGy was needed for radiation sterilization of canned cooked beef containing 10" spores of the most radiation resistant strain of C. botulinurn. Our values for B. cereus were also near those reported by Grecz et al (1965) for cooked ground beef containing C. botulinum irradiated at 0°C.…”

Statistical Estimation of 12d for Radappertized Foods

“…A typical set of experimental results (Anellis and Werkowski, 1968) is reproduced in Table 1. It is clear from this and other data (Anellis et al, 1969;1972;Grecz et al, 1965;Segner and Schmidt, 1966), that the estimate of D increases very markedly as x increases. This trend is unambiguous and far too pervasive t o be attributed t o any sort of randomness.…”

Cryogenic gamma irradiation of prototype pork and chicken and antagonistic effect between Clostridium botulinum types A and B

“…Radiation dose-survival curves reported for C. botulinum spores suspended in foods (12,13,19,27,30,39), broth (14,15,18,39,42), phosphate buffer (5, 12, 17, 19, 24, 27-29, 39, 42), or water (1, 32, 35, 36, 40, 44) invariably followed a shifted exponential distribution, whether the test organism was used as an individual strain of type A, B, E, or F or was a mixed inoculum of five type A and five type B in foods (12,30). In view of such weighty, although circumstantial, experimental evidence to support the statistical evaluations, it seems more reasonable to base the 12D estimations on the shifted exponential mode of death kinetics instead of on the prior, arbitrarily agreed simple exponential form.…”