Studies on Microorganisms in Simulated Room Environments

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Abstract
A method previously described was applied to the detn. of the death rates of streptococci in the presence of daylight, sunlight and artificial light under simulated room conditions. Daylight passing through glass on clear or cloudy days is a potent lethal agent for streptococci. Analysis of a number of tests on a short-chain [alpha] hemolytic strain indicated that (1) the death rate was geometric; (2) the 50% survival time occurred in about 45 min.; (3) the lethal effect per foot-candle of daylight varied with the character of the sky, blue skies with no or few clouds yielding a maximal value and completely gray skies a minimal one; (4) the overall potency of all types of sky, except completely overcast, and dark ones, was very similar; the increased reflection from clouds compensated to a great extent for the loss of the more active blue light by the latter. Daylight destroyed 50% of the chains of a short-chain Group B [beta]-hemolytic strain in about 1 hr. and the rate appeared to be geometric. However, under the same conditions a long-chain Group A [beta]-hemo-lytic strain apparently was more resistant to daylight and did not yield a geometric death rate. These differences were ascribed to the long chain length of this strain. Sunlight passing through a window was about ten times as lethal as daylight for the a-hemolytic strain; the 50% survival time was calculated to be about 5 min. However, daylight from blue skies appeared to be somewhat more potent per foot-candle than was sunlight. This may be ascribed to the small amt. of blue light in the latter. Artificial light (fluorescent lamp) was less lethal per foot-candle for the same strain than was light from a blue sky but about as effective as sunlight. Because of the low intensities employed in this type of illumination its practical value is questionable. Some possible public health implications of the findings are discussed.

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