Fig 1.

Evolution of multidrug resistance in experimental populations of Pseudomonas aeruginosa treated with multidrug therapy. Multidrug treatments were as follows: rifampin and streptomycin simultaneously (filled circles), sequential therapy with exposure to streptomycin first (filled triangles), and sequential therapy with exposure to rifampin first (filled squares). For sequential therapy, the antibiotics were switched on a daily basis. Populations were grown in the absence of immigration (A), or with 1% (B) and 10% (C) immigration. Resistance was measured as average density (OD₆₀₀) of the selection lines at the end of each transfer. Error bars represent standard errors of the means.