FIG. 2.

Modeled antibiotic resistance levels for the combination of a multicomponent efflux pump with a single-component pump. The axis next to the solid arrow represents the level of resistance conferred by the multicomponent pump alone, while the dashed arrow indicates the resistance due to the single-component pump; the ranges have been selected arbitrarily. The axes are graded in units of fold increase of inhibitory drug concentrations conferred by the pumps. The surfaces represent the levels of resistance conferred by the two pumps combined. In panel A, substrate capture by the multicomponent pump is assumed to occur in the cytosol, and the area has been calculated using equation 12. In panel B, periplasmic substrate capture is assumed, and equation 14 has been used. Only periplasmic substrate capture results in a multiplicative action of the two pumps.