Strain-to-strain variations in the virulence level of S. pneumoniae. (A) Schematic workflow of systemic assessment of the virulence levels of pneumococcal isolates in murine sepsis model. (B) Survival (left) and bacteremia (right) levels of CD1 mice infected i.p. with 104 CFU of representative HV (red line) and LV (green line) pneumococcal isolates. Serotype of each strain is denoted with superscript characters. n = 5–6. ND, not detected. (C) Bacteremia kinetics of the 48 HV (left) and 96 LV (right) strains 12 and 24 h after infection as in B. Each dot represents the mean value of five to nine mice for one strain. Lined dots indicate the values for the same strain at two time points. (D) Mean survival time of the mice infected with the same HV and LV strains as in B. Each dot represents the mean value for one strain. (E) Correlation between pneumococcal serotypes and mean survival times of mice infected as in B. The number of strains tested for each serotype is indicated at the right. All data were pooled from two independent experiments. Unpaired t test (D), ****, P < 0.0001.
