The Effects of Ultraviolet Light on Bacteria Suspended in Air

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Abstract
Bacteria suspended in air were irradiated with u.-v. (2537 A) and the survivors examined and counted by means of an air-tube apparatus previously described in which the organisms pass close to a low-pressure mercury discharge lamp. Minor improvements in the apparatus and technique are given here together with new data. Lethal energies measured in ergs/cm2 are as follows Staphylococcus albus 23,300, S. aureus 26,500, Escherichia coli 24,800, Serratia marcescens 20,700, Pseudomonas aeru-ginosa 16.100, Bacillus sub tills 62,200 (old culture containing spores). Further experiments on E. coli gave a survival ratio vs. incident energy curve departing markedly from the log curve (Log N/No=-[long dash]KE) to be expected from the single-hit hypothesis. Ps. aeruginosa survivors produced a rather high percentage of temporarily colorless colonies; controls did not. This suggests that some hits are not fatal. Both findings suggest that photosterilization is more complicated than a single-hit theory or even a multiple-hit theory can explain without taking into account individual differences in cell resistance.