Figure 5.
Pre-existing immunity to L. monocytogenes 10403S provides limited protection to challenge with outbreak strain LS741. BALB/c mice were immunized with approximately 0.1 LD50 of the indicated strains (1 × 103 CFU of 10403S or 300 CFU of LS741) or PBS. Twenty-eight days later, immunized mice were challenged with 1 × 105 CFU of the indicated strains. At 48 hours post-challenge, mice were euthanized and the spleen (a), liver (b) and brain (c) of each mouse was collected and the bacterial burden determined. Horizontal lines indicate median values. The Mann–Whitney test was used to assess statistical significance between bracketed groups: *P < 0.05, **P < 0.01, ns = not statistically significant (P = 0.45). The dotted line in panel c indicates a limit of detection of 10 CFU per brain.