FIG 4.

Three-dimensional synergy. The combinatorial effects of azithromycin, minocycline, and rifampin were tested against intracellular growth of L. pneumophila. The plotted surface contour overlies data points for antimicrobial combinations with <99% intracellular growth inhibition relative to that of the uninfected control wells. A high degree of surface concavity suggests three-dimensional synergy. Concentrations along axes are in nanograms/milliliter. A representative experiment is shown; the data set used for graph generation was based on 512 antimicrobial combinations tested in triplicate.