Effect of sorbed water on the death rate of washed Serratia marcescens.

In a previous paper (Monk et al., 1956) on the effect of water on the death rate of Serratia marcescens, a particularly lethal effect was found at a water content of about 50 per cent in the mixture of cells and additives. Since the vapor pressure characteristics of the cells and each of the components was not known in detail it was not possible to determine how much of this water was in the cells and whether the rapid loss of viability was due to a toxic effect of some component. This paper describes an experimental determination of the logarithmic death rates of this organism after rewetting to various water contents following lyophilization of washed cells. It was hoped that measurements of the stability in the absence of salts and other materials ordinarily present or deliberately added would indicate if different degrees of wetting would in itself be toxic to bacteria.