RELATIVE HUMIDITY AND THE KILLING OF BACTERIA. THE SURVIVAL OF DAMP SERRATIA MARCESCENS IN AIR
ARMY BIOLOGICAL LABS FREDERICK MD
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The viability of washed moist cells of Serratia marcescens after storage has been measured in relation to variations in the prior treatment of the cells and in conditions of storage. The factors considered were 1 water content during storage 2 method of arriving at water content partial drying in vacuum or freeze-drying and addition of water 3 presence or absence of air during storage. Increasingly rapid decay occurs as the water content at which the cells are stored is diminished from above 90 to 20 or 30 critical water content. It occurs in presence or absence of air and it occurs whether the final water content is approached by removal of water from wet cells or by addition of water to freeze-dried cells. The rate of decay during storage at 20 to 30 water is somewhat diminished by the presence of air protective effect of air. As the water content is further reduced to less than 10, the stability of cells stored in a vacuum approaches that of wet cells. In presence of air the reverse is true the stability decreases until at less than 1 water, the decay rate is about as great as at the critical water content toxic effect of air. Particularly rapid decay of S. marcescens at the critical water content has escaped attention in aerosol studies because accurate control of relative humidity RH in this region, RH 94 to 99, is virtually impossible in such studies. On the other hand, values of decay rates referred to measured water contents are quite unreliable in the 20 to 80 RH zone because the corresponding variation of water content is too small to measure reliably.