Figure 6
Serotype switching does not impact strain virulence. (a–d) Survival of CD1 mice inoculated by intraperitoneal injection with either 5 × 107 CFU of serotype 2 (a) or 1/2 (b) strains or with either 1 × 108 CFU of serotype 14 (c) or 1 (d) strains. In all cases, Log-Rank (Mantel-Cox) test revealed no significant differences in survival rates between the field parental strains and derivative mutants. All control animals injected with vehicle (Todd Hewitt Broth) survived the trial (data not shown for simplicity). (e–h) Bacterial load in blood was evaluated in all groups by drawing 5 μl of blood from the tail vein of mice followed by plating and enumeration (see methods). (e) Serotype 2 field strain and derived mutant SS2to1/2. (f) Serotype 1/2 field strain and derived mutant SS1/2to2. (g) Serotype 14 field strain and derived mutant SS14to1. (h) Serotype 1 field strain and derived mutant SS1to14. No significant differences in bacterial load were observed between parental strains and their corresponding mutants (Mann-Whitney Rank Sum test, P < 0.05).
