The Preservation of Pneumococcus by Freezing and Drying

Swift (1937) has shown that when streptococci are completely dried while in the frozen state, they will survive unchanged for many years. Since pneumococci are more sensitive to chemical changes in their environment and undergo spontaneous autolysis more readily than do streptococci, it was of interest to determine how long pneumococcal cells would remain viable when kept in the desiccated state. In order to ascertain whether this method of preservation, which has proved so practical in the case of other bacteria, is equally applicable to pneumococci, the following experiments were carried out. During the winter of 1935-1936 freshly isolated strains of types I, II, III and VIII pneumococci were prepared and dried by the technic described by Swift. The viability of the bacterial cells preserved under these conditions was tested by cultural methods after a period of three years. The biochemical and immunological characteristics, as well as the virulence of the recovered cultures, were compared with those of the parent strain. METHODS Strains of pneumococcus of types I, II, III, and VIII freshly isolated from human sources and of known virulence were grown in flasks containing 50 ml. of blood broth for 18 hours at 370. The cultures were centrifuged and the cells resuspended in 1 ml. of plain broth. Two-tenths ml. portions of the concentrated bacterial suspension were distributed in small glass tubes meas-