Effect of Gamma-ray upon Food Microorganisms

Studies concerning Gamma-ray Resistivity of Escherichia coli (III)

Abstract

(1) When samples containing E. coli were irradiated with gamma-ray in various types of media, survivals obtained from each sample were different from one another. Survivals obtained from a broth agar medium were highest, those from a synthetic medium covered with a broth agar prior to incubation followed, while those from the synthetic medium were least. And, survivals of a pure agar medium which was covered with a nutrient medium after irradiation were lower than those from the above-mentioned media. Among two nutrient media, survivals of a pure agar medium covered with a broth agar were higher than those covered with a synthetic medium.
(2) Gamma-ray irradiated cells of E. coli markedly decreased the ability to exhibit them-selves in the number of colonies in the syn-thetic medium as compared with broth agar medium.
(3) When E. coli was preserved at room temperature in a broth agar medium or a synthetic, non-nutrient, medium prior to gamma-ray irradiation, in both cases it was observed the longer the preservation period, the more cells of the strain survive. However, the reasons for each case are not identical. It is therefore necessary to apply gamma-ray irradiation upon the experimental sample im-mediately after solidification of the used medium.
(4) In case of using gamma-ray at dose-rates ranging between 4000 and 14000 rep/h, survival-ratios obtained from irradiated samples at an irradiated dose of 15000 rep resulted to have the same value of 30%.
(5) Also, in case of applying a gamma-ray dose-rate exceeding 4, 000 rep/h, there was no time-factor within a certain time-range of 1 and 4 hours.