CULTURAL CONDITIONS AS DETERMINANTS OF SENSITIVITY OF ESCHERICHIA COLI TO DAMAGING AGENTS

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Abstract
The effect on several strains of E. coli of X-rays, UV and heat inactivation is greatly modified by changes in composition of the growth medium. Cells grown in peptone are small and more sensitive to each type of inactivation, while cells grown in peptone plus any of a number of sugars are larger and more resistant. In X-ray inactivation, the final pH of the growth medium is directly related to the sensitivity of the cells. The relative amounts of deoxyribonucleic acid per cell of resistant and sensitive cells does not accord with the suggestion that the cells differ in ploidy or numbers of nuclei. The sigmoid survival curves for resistant cells cannot be accounted for on the basis of a gross structural abnormality such as multicellular or multinuclear condition, or on the basis of plating artifacts such as clumping. The hydrogen ion concentration or composition of the irradiation medium, with or without prior incubation, has no detectable effect on either sensitive or resistant cells.