FIGURE 2. Rescaling of effective drug concentrations by resistance generates a region exclusive to growth of sensitive bacteria in a suppressive drug combination.

From the following article:

Antibiotic interactions that select against resistance

Remy Chait, Allison Craney & Roy Kishony

Nature 446, 668-671(5 April 2007)



ad, MIC lines (green, sensitive strain Wyl; red, doxycycline-resistant strain t17yl) and higher growth rate isoboles (grey scale) in synergistic (doxycycline–erythromycin (a, b)) and suppressive (doxycycline–ciprofloxacin (c, d)) drug combinations. The MIC lines of the sensitive and resistant strains are similar, except for a rescaling in doxycycline concentrations (linear scales in b and d). In the synergistic case (a), this scaling leaves the growth region of the sensitive strain fully enclosed by that of the resistant strain. In contrast, in the suppressive case, the scaling generates a region in which only the sensitive strain grows (c, asterisk). Growth rates were measured at an array of drug concentrations indicated in b and d (green points, sensitive; red points, resistant) by c.p.s. of bacterial luminescence versus time (see Methods). e, Sample growth curves of the sensitive strain at four conditions indicated in d: no drug (black), doxycycline only (cyan), ciprofloxacin only (magenta) and the combination (blue). Two replicates and their linear fit (grey lines) are shown.

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