FIG. 3.

Competitive index assay analysis of primary and secondary infection with wild-type and ΔlemA mutant L. monocytogenes. Groups of four to six naïve and Listeria-immune mice were infected with a 1:1 mixture of DP-L3903 (wild type) and NR1-1578 (ΔlemA). Mice were sacrificed 3 days after primary infections (0.1 LD₅₀ of total bacteria) or 2 days after secondary infections (0.1 LD₅₀ of wild-type listeriae followed by 5 LD₅₀ of total bacteria 3 weeks later). Spleens and livers were harvested and homogenized, and dilutions were plated on BHI agar with or without erythromycin. A competitive index of 1.0 indicates that the two strains were recovered in equal numbers. Data compiled from three separate experiments are shown; bars indicate average values for each experimental group. *, P < 0.01 as determined by a two-sided Mann-Whitney test.