Inactivation of the Radiation-Resistant Spoilage Bacterium Micrococcus radiodurans

Abstract

of the radiation-resistant spoilage bacterium Micrococcus radiodurans. II. Radiation inactivation rates as influenced by menstruum temperature, preirradiation heat treatment, and certain reducing agents. Appl. Microbiol. 11:413-417. 1963.-The R1 strain of Micrococcus radiodurwans, previously determined to be more resistant than three other strains exposed to gamma radiation, was studied further to determiine the influence of certain environmental factors on resistance to radiation inactivation. The frozen state offered insignificant protection to the organisms irradiated in raw pureed beef. Resistance was reduced by higher menstruum temperatures (40 and 50 C) during irradiation. Preirradiation heat treatment was found to lower resistance to subsequent irradiation. When the cells were irradiated in buffer at pH 5, 7, or 9, no differences in resistance were noted. Cell suspensions in buffer were protected to some extent by cysteine but not by thioglycolate. Ascorbate enhanced radiation inactivation. Earlier papers have described the radiation-resistant spoilage organism MIicrococcus radiodurans (Anderson et al., 1956; Anderson, Rash, and Elliker, 1961; Duggan et al., 1959; Raj et al., 1960). The R1 strain of this organism, which has been shown to be more resistant than the other cultures examined (Duggan, Anderson, and Elliker, ' This paper reports research undertaken in cooperation with the Quartermaster Food and Container Institute for the Armed Forces, Q. M. Research and Engineering Command, U.S. Army, and has been assigned no. 2239 in a series of papers approved for publication. The views or conclusions contained in this report are those of the authors. They are not to be construed as necessarily reflecting the views or endorsements of the Department of Defense. 2 Technical Paper no. 1598, Oregon Agricultural Experiment Station; contribution of the Department of Microbiology. I Presented at the 62nd Annual Meeting of the American Society for Microbiology, Kansas City, Mo., 8 May 1962.

Inactivation of the Radiation-Resistant Spoilage Bacterium Micrococcus radiodurans

“…However, upon irradiation at the nondestructive substrate temperature of 40 C (104 F), the cells appeared to be much more susceptible to radiation kill (Tables 1 and 4). Irradiation at the destructive temperature (Duggan et al, 1963b) of 50 C (122 F) also increased susceptibility to radiation inactivation over that at normal temperatures (Tables 1 and 4). Since no survival was detected in any of the replicates irradiated at the higher temperatures, no definite surviving fractions are available.…”

“…A preirradiation heat treatment was carried out in small-bore tubes (5-mm outer diameter, 1-mm wall thickness) as described elsewhere (Duggan, Anderson, and Elliker, 1963b). Four of these "thermal death rate" tubes were filled with 1 ml of the beef suspension of R1 culture, sealed with sealing wax, immersed in a water bath (57.2 C) for 2.5 min, and then removed into ice water.…”

Inactivation of the Radiation-Resistant Spoilage Bacterium Micrococcus radiodurans

“…described above, could not be accounted for by multicellularity. Exponential thermal resistance curves were obtained with M. radiodurans (Duggan, Anderson, and Elliker, 1963b) when the cells and menstruum were prepared in a manner identical with those used for these radiation survival curves, indicating that the cells were probably well-dispersed in the menstruum. The degree of packet or clump formation that would be required to account for a lag of the magnitude obtained with M. radiodurans would be unrealistic.…”

Sterilization of laboratory animal diets using gamma radiation

“…2 with respect to the latter, for example, that a dose of 0.6 Mrad would be expected to reduce a population of Salmonella typhimurium in frozen meat by a factor of about 105. Not all the curves obtained are as linear as those iUustrated, quite commonly an initial 'shoulder' on the curve is apparent; the high resistance of Micrococcus radiodurans is seen as a very wide shoulder which can extend up to a dose of 2 Mrad, depending on the suspending media (Duggan, Anderson & Elliker, 1963). Certain strains of Streptococcus faecium also show high resistance, non-linear curves being obtained over the wide dose range studied (Chdstensen, 1964).…”