Spent filtrate supplementation results in increased detection of <i>F. tularensis</i> in mixed cultures.

<p><b>A)</b><i>F. tularensis</i> was spiked in a ten-fold serial dilution in 10⁹CFU/mL of soil bacteria or inoculated as a pure culture and incubated in control broth (TSB with 0.1% L-cysteine) or spent filtrate (composition: TSB and 0.1% L-cysteine and 10% spent culture filtrate) overnight at 37°C with 120 rpm shaking speed. <b>B)</b><i>F. tularensis</i> (1–10² cells/mL) was spiked in 10⁹CFU/mL of lettuce bacteria. Supplementation of TSB and 0.1% L-cysteine with spent culture filtrate resulted in <i>F. tularensis</i> detection at all inoculums (1–10² cells/mL). Control medium combined with lettuce showed Cp values greater than 34 and were considered negative for <i>F. tularensis</i>. All samples were conducted in triplicate with technical triplicates. Legend: Control = white bar, Spent filtrate = black bar, Control and soil bacteria = dark grey bar, and Spent filtrate and soil/lettuce bacteria = light grey bar.