FREE RADICAL FORMATION AND SURVIVAL OF LYOPHILIZED MICROORGANISMS.

Heckly, Robert J. (University of California, Berkeley), R. L. Dimmick, and J. J. Windle. Free radical formation and survival of lyophilized microorganisms. J. Bacteriol. 85:961-966. 1963.-A correlation between death and spontaneous free radical production, measured by an increase in the relative electron paramagnetic resonance (EPR) signal, was shown to exist for several species of microorganisms stored in the freezedried state, but the relationship between the free radical concentration and number of dead cells was not a simple proportion. Lactose added to Sarcina lutea reduced radical production and increased stability when dry preparations were stored in air. Death and free radical formation were more extensive when lyophilized Streptococcus lactis cultures were stored in air than in vacuum. Free radicals were also produced by dry yeast. Few, if any, free radicals were produced by bacteria or yeast stored in vacuum. It was shown that the observed free radical production was not caused by exposure to light. The EPR signal produced by dry Serratia marcescens decreased rapidly when cells were exposed to a humid atmosphere but the EPR signal slowly increased after cells were redried and exposed to oxygen.