Fig. 3.
The effect of pH on the antibacterial activity, positive charge, drug uptake, and time-kill kinetics of apramycin, gentamicin, and amikacin in the uropathogen E. coli J96.(a) MICs for E. coli J96 at pH7.4, pH6.0, and pH5.0. (b) Net positive charge of apramycin, gentamicin, and amikacin when applying the Henderson-Hasselbalch equation to the pKa values of individual amines published previously. (c) Cytoplasmic uptake of apramycin, gentamicin and amikacin by E. coli J96 cells at pH 5.7, pH 6.5, and pH 7.3 quantified by LC/MS/MS following cellular fractionation of 3.9 × 109 cells. Data blotted as mean ± SD of n = 4 replicates. (d-f) Time-kill kinetics of apramycin (d), gentamicin (e), and amikacin (f) against E. coli J96 at a drug concentration of eight times the MIC at neutral pH: 32 μg/mL apramycin, 4 μg/mL gentamicin, and 16 μg/mL amikacin, respectively.