SYNERGISTIC LETHAL ACTION OF ULTRAVIOLET‐VIOLET RADIATIONS AND MILD HEAT IN ESCHERICHIA COLI

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Abstract
Abstract— The lethal interaction of far ultraviolet (254nm), near ultraviolet (334 and 365nm) and violet visible (405nm) radiation treatment with mild heat treatment was studied. Except at 254nm, a strong positive radiation dose‐dependent interaction (synergism) was always observed. The efficiency of sensitisation to heat, as a function of dose at each wavelength, was found to be directly correlated with the dose necessary to eliminate the shoulder from the survival curve of a repair proficient strain but was apparently unrelated to the relative near‐ultraviolet sensitivities of a repair deficient strain. The interaction was independent of the order of treatments. A radiation dose of 106 Jm‐2 at 365nm slightly sensitised a cell population to 45°C incubation (normally non‐lethal) and strongly sensitised the cells to 48°C treatment (normally 80 percent survival after 2 hours). It is proposed that in addition to DNA damage, both heat treatment and near ultraviolet treatment interfere with DNA recovery mechanisms so that the combination of the two agents inevitably leads to a strong positive interaction.

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