Figure 2.

pH-dependent bactericidal activity of glycolic acid against C. acnes. The pH-dependent reduction in viable C. acnes cell concentration is plotted as a function of glycolic acid concentration. The data correspond to (a) pH 2.5, (b) pH 3.0, (c) pH 3.5, and (d) pH 4.0. The C. acnes cell concentration was 1 × 10⁶ CFU mL⁻¹. The recorded MBC values are 12.5 mM, 25 mM, and 50 mM at pH 3.0, 3.5, and 4.0, respectively, and correspond to the lowest glycolic acid concentration at which no bacterial cell viability was detected (reported as ND, not determined). C. acnes cells were not viable after incubation in the pH 2.5 condition, whereas viability was maintained after incubation in the other test pH conditions as indicated by the 0 mM glycolic acid control data for each case. Mean ± standard deviation values are reported from n = 3 experiments.