Hill functions for two-drug combinations and the constituent individual antibiotics (<i>E. coli</i>).

<p>Each graph shows the Hill functions for a drug combination and the constituent single drugs with drug concentrations normalized as multiples of Cidal Units (xCU). Error bars represent the standard errors for the growth/death rate at each antibiotic concentration. (a) ampicillin (AMP), ciprofloxacin (CIP), and ampicillin+ciprofloxacin (b) ampicillin, tetracycline (TET), and ampicillin+tetracycline (c) ciprofloxacin, tetracycline, and ciprofloxacin+tetracycline (d) ciprofloxacin, tobramycin (TOB), and ciprofloxacin+tobramycin (e) tobramycin, ampicillin, and tobramycin+ampicillin (f) tobramycin, tetracycline, and tobramycin+tetracycline.