FIG. 5.

Expression levels of genes of the SsrAB virulon in intracellular bacteria. RAW264.7 macrophages were infected at an MOI of 10 (A) or 50 (B) with various Salmonella strains harboring reporter gene fusions, as indicated, or the WT strain without the reporter (no luc). Noninternalized bacteria were killed by the addition of gentamicin. Infected host cells were lysed 8 h after infection (p.i.), intracellular bacteria were recovered, and the luciferase activities were quantified. In parallel, aliquots of the lysates were plated on agar plates for the determination of the number of intracellular bacteria (cfu). The numbers of intracellular bacteria recovered 8 h after infection are shown by circles. The expression of various genes of the SsrAB virulon was calculated as RLU per CFU. Means and standard deviations of triplicates are shown for an experiment representative of three independent assays. Reporter activities for several strains (indicated by asterisks) were close to the limit of detection of the assay.