VIRULENCE OF STREPTOCOCCUS-PNEUMONIAE IN MICE - A STANDARDIZED METHODFOR PREPARATION AND FROZEN STORAGE OF THE EXPERIMENTAL BACTERIAL INOCULUM

Animal models of pneumococcal infection a re important to evaluate the protective capacity of new vaccine candidates. We have established a method to prepare and store the experimental inoculum without loss of virulence or number of bacteria. This allows a standardized inoculum f rom the same culture batch to be used in several experiments. Pneumoco cci were cultured to mid-logarithmic growth phase in Todd-Hewitt broth with 17% fetal calf serum. The bacterial broth was distributed into s maller volumes and immediately frozen on liquid nitrogen and stored at -70 degrees C. We have tested the virulence of five different pneumoc occal serotypes in BALB/c, C57 BL/6, and NIHS mice using inocula prepa red by this method and stored without loss of virulence for up to 4 ye ars. Serotypes 1, 4, 5 and 8 were highly virulent for the strains of m ice tested whereas type 6B showed lower virulence and a peculiar, prot racted course of infection. There were no clear differences in virulen ce between the different strains of mice with the exception of serotyp e 6B, which showed higher virulence in BALB/c and NIHS mice than in C5 7BL/6 mice.