Figure 3: Treatment of Y. pestis pgm- with 25 μM PMA and B. anthracis Sterne with 10 μM PMA is most effective for distinguishing cell viability. Titration of PMA with (A) Y. pestis pgm- cells and (B) B. anthracis Sterne vegetative cells followed by a five minute exposure to the LED PMALiteTM and detection by qPCR. ND indicates lack of qPCR signal. Cell counts were determined by dilution series plating qPCR reaction. Measurements are the average value of three independent experiments, with three technical replicates in each independent experiment, and error bars are representative of the standard deviation. The * symbol indicates a statistically significant difference (p < 0.05) when comparing the ΔCT values of viable and nonviable populations. For every experiment, the total number of cells was determined by plate counts. Among the three independent experiments, the total number of cells per qPCR reaction for B. anthracis Sterne ranged from 5.8 × 103 to 1.33 × 104 which corresponded to CT values of 26.2 to 27.1. For Y. pestis, the total number of cells per qPCR reaction ranged from 6.1 × 105 to 9.8 × 105 which corresponded to CT values of 15.7 to 16.1.