FTL_1581 contributes to F. tularensis LVS virulence. (A) A schematic of FTL_1581 protein is depicted showing domains predicted by PROSITE. (B) Competition studies in the chicken embryo infection model using a mixture of LVS and 1581d (1:1 based on OD600; viable bacteria in the inoculum were quantified by diluting and plating the input). Competition ratios (1581d: LVS) were normalized to the input to account for differences in the inoculum. These ratios were analyzed for statistical significance by Chi square; P < 0.001 at days 1, 2, and 3 post-infection. Data are mean competition ratio ± SEM of three embryos per time point within one experiment and are representative of duplicate experiments. (C) Macrophages were infected with LVS, 1581d, or 1581d/pFTL_1581 and were lysed at the indicated times. Data are mean ± SEM of triplicate wells within one experiment and are representative of four experiments performed using cells from separate donors. Following log transformation, differences in CFU were determined by a Student's t-Test in which P = 0.003 at 24 h.