FIG 2.

L. pneumophila cell density has a large impact on HGA and H₂O₂ susceptibility. (A) HGA kills low-density bacteria (triangles) at ~5,000× lower concentration than that required to kill high-density cells (squares) after 24 h. Shaded regions show the differences in inhibitory concentrations between high- and low-density Legionella for each compound. (B and C) Density-dependence of Legionella susceptibility to H₂O₂ (B) and, to a lesser extent, bleach (C). (D through F) Legionella susceptibility to various antibiotics shows a more typical inoculum effect. In panel F, where solubility issues limited our ability to kill high-density cells below our limit of detection, we highlight the amount of drug required to kill 99% of the starting bacterial population. All experiments incubated bacteria with antimicrobial compounds in PBS for 24 h.