Bacterial killing by primary human macrophages. The ability of primary human macrophages to kill E. coli strain DH5α (E. coli) was compared to five H. pylori isolates (NL101, NL103, NL106, NL107 and SS1). The number of viable bacteria recovered from macrophages 30 minutes (open bars) two hours (blue bars), eight hours (grey bars) or 24 hours (closed bars) after infection is represented in colony forming units per millilitre (CFU/mL). Infected macrophage cultures were extensively washed to remove extra-cellular bacteria. Data is the mean of three independent experiments.