Fig. 4.

An FMN and FAD auxotrophic L. monocytogenes strain is restricted to intracellular growth in vivo. (A) Bacterial burdens in the gallbladder of CD-1 mice infected intravenously with 1 × 10⁵ CFUs of indicated L. monocytogenes strains. At 48 h postinfection, the gallbladders were harvested, homogenized, and plated to determine the CFUs per organ. The data show the combination of at least two independent experiments: WT and ΔribCΔribF (n = 30 mice), ΔribC and ΔribF (n = 15 mice), and ΔribCΔribF + ribC (n = 10 mice). The black lines represent the median CFUs for each strain. The dashed line represents the limit of detection. Statistical significance of logarithmically transformed CFU values was determined using one-way ANOVA and Dunnett’s posttest using WT as the control. ****P < 0.0001; ns, not significant, P > 0.05. (B) In vitro growth of L. monocytogenes strains in defibrinated sheep’s blood. Bacterial growth was determined by plating at the indicated times to determine the total CFUs in blood. The means and SEMs of three independent experiments are shown. (C) Bacterial burdens in the GI tract of CD-1 mice infected orally with 1 × 10⁸ CFUs of indicated L. monocytogenes strains. Mice were pretreated orally with streptomycin prior to the infection. Stool samples were collected from day 1 to day 5 and plated to determine the CFUs per gram of stool. The data show the means and SDs of the mean from a combination of three independent experiments, n = 15 mice per L. monocytogenes strain. The dashed line represents the limit of detection.