Dose-response plot of Y. pestis growth as a function of FR900098 concentration.

Fractional growth is calculated as the ratio of cell density (OD600) in the presence of inhibitor to cell density in the absence of inhibitor. Nonlinear regression fitting was performed, resulting in an IC50 of 29 µM (6.4 µg/mL). The goodness-of-fit (R2) value is indicated. For comparison, the IC50 of ampicillin is 10.8 µM (3.8 µg/mL; see Figure S1).