Fig. 3.

Intracellular growth of different strains of F. tularensis. J774 cells (A) or PECs (B) were infected by various strains of F. tularensis at an MOI of 200 for 2 h. Upon gentamicin treatment, cells were allowed to recover for 30 min, after which they were lysed immediately (which corresponds to 0 h) or after 24 h or 48 h with PBS-buffered 0.1% sodium deoxycholate solution and plated to determine the number of viable bacteria (log₁₀). All infections were repeated two to three times with triplicate data sets. Representative experiments for strain LVS and derivatives thereof and F. tularensis subsp. novicida U112 and derivatives thereof are shown. Each bar represents the mean values, and the error bar indicates the standard deviation. The asterisks indicate that the log₁₀ number of CFU was significantly different from that for the parental strain (LVS or U112), as determined by a 2-sided t test with equal variance (*, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001).