Figure 4: Non-selective toxins can substantially modify the selection on resistance by an antibiotic diffusing from a local source.
From: Pervasive selection for and against antibiotic resistance in inhomogeneous multistress environments
(a) A diffusing gradient of doxycycline alone selects strongly for tetracycline resistance at higher concentrations and is neutral at lower levels (Inset, −Cpr). A small inhibitory level of ciprofloxacin added uniformly to the agar (+Cpr) drastically changes the pattern of selection by doxycycline, revealing a large band of selection for sensitivity (green circle), a band of selection for resistance (red circle), and multiple regions of inhibition of both strains (black regions). (b) Since ciprofloxacin and doxycycline interact suppressively, we rationalize this picture by comparing the sampled gradient in the image (a) with a schematic of such a suppression interaction (compare blue dashed wedges), that similarly crosses regions of threshold selection for tetracycline resistance and sensitivity.
