Consider a bacterial population with three subpopulations characterized by MIC isoboles: the wild-type (solid line), a mutant population resistant only to drug X (dashed line), and a mutant population resistant only to drug Y (dotted line). In this simple scenario, without double mutants or cross-resistance, one mutation renders resistance to only drug X and another mutation renders resistance to only drug Y. The mutant prevention concentration (MPC) line is shown by the outermost isobole, and the MSW is shown by the shaded area between the outermost and innermost isoboles. The MSW is larger in the synergistic combination than in the suppressive combination.