Figure 4. Inhibition of intracellular F. novicida replication in two cell lines following treatment with selected compounds.

Cell lines were first infected with F. novicida at an MOI of 500. The cells were treated with the following concentrations of antibiotics. The cells were lysed after 20 hours of treatment and the intracellular bacteria were enumerated. A) Inhibition of intracellular F. novicida in A549 cells with fosmidomycin (Fos), FR900098 (FR), or compound 1 (C1) for 20 hours. Each compound was tested at 250 µM and at 2× MIC (2× MIC for fosmidomycin = 250 µM, 2× MIC for FR900098 = 500 µM and 2× MIC for compound 1 = 400 µM). All three compounds significantly inhibited intracellular F. novicida growth. At 250 µM, intracellular growth was inhibited 98.0±0.7% by fosmidomycin, 86±6% by FR900098, and 97.0±0.8% by compound 1. At 2× MIC, FR900098 (500 µM) inhibited 85±10% of intracellular growth, while compound 1 inhibited 99.0±0.7% of intracellular growth. B) Inhibition of F. novicida in RAW264.7 cells with fosmidomycin, FR900098, and compound 1 for 20 hours. Similar results were seen for the RAW264.7 cells as were seen for the A549 cells. C) Inhibition of the F. novicida glpT mutant intracellular replication in A549 cells. The intracellular-replication inhibition experiment was performed using the glpT mutant as previously described for wild-type F. novicida. Replication of intracellular glpT mutant was not affected by fosmidomycin (250 µM) and FR900098 (500 µM), but was susceptible to compound 1 (400 µM).