FACTORS AFFECTING THE VIABILITY OF AIR-BORNE BACTERIA: IV. THE INACTIVATION AND REACTIVATION OF AIR-BORNE SERRATIA MARCESCENS BY ULTRAVIOLET AND VISIBLE LIGHT

Abstract

The effect of ultraviolet and visible light on air-borne Serralia marcescens has been studied. It was found that prolonged exposure to 3400–4500 Å and 5200–5800 Å radiations can be lethal to air-borne cells. Also, both wavebands were able to photoreactivate cells irradiated with U,V. light of 2800–3200 Å. The U.V. exponential death rate was not observed with visible light and a lag phase of from 15 to 20 minutes was encountered before any deaths occurred. Red dyes, of the alizarin type, were found to desensitize cells to U.V. irradiation damage, whereas blue and yellow dyes sensitized them. The effects of U,V. and visible light were additive when used simultaneously, but reactivation occurred when cells were exposed to the visible light immediately after U.V. irradiation. A mechanism, based on the long-distance transfer of excitation energy, is outlined and offered as a possible explanation for these experimental results, and for those of other workers on the inactivation and photoreactivation of microorganisms.