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Appl Environ Microbiol. 1963 September; 11(5): 398-403

Inactivation of the Radiation-Resistant Spoilage Bacterium Micrococcus radiodurans

I. Radiation Inactivation Rates in Three Meat Substrates and in Buffer^1,2,3

Department of Microbiology, Oregon State University, Corvallis, Oregon

ABSTRACT

A simplified technique permitting the pipetting of raw puréed meats for quantitative bacteriological study is described for use in determining survival of these non-sporing bacteria, which are exceptionally resistant to radiation. Survival curves, using gamma radiation as the sterilizing agent, were determined in raw beef with four strains of Micrococcus radiodurans. Survival curves of the R₁ strain in other meat substrates showed that survival was significantly greater in raw beef and raw chicken than in raw fish or in cooked beef. Resistance was lowest in the buffer. Cells grown in broth (an artificial growth medium) and resuspended in beef did not differ in resistance from cells that had been grown and irradiated in beef. Survival rate was statistically independent of the initial cell concentration, even though there appeared to be a correlation between lower death rate and lower initial cell concentrations. The initial viable count of this culture of the domesticated R₁ strain in beef was reduced by a factor of about 10^-5 by 3.0 megarad, and 4.0 megarad reduced the initial count by a factor of more than 10^-9. Data suggest that M. radiodurans R₁ is more resistant to radiation than spore-forming spoilage bacteria for which inactivation rates have been published.

⁴ Present address: Department of Microbiology, University of Kansas Medical Center, Kansas City.

¹ 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. 2251 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. 1597, Oregon Agricultural Experiment Station, contribution of the Department of Microbiology.

³ Presented at the 62nd Annual Meeting of the American Society for Microbiology, 8 May 1962, Kansas City, Mo.