Clinical isolates of P. acnes are sensitive to chitosan. Chitosan was incubated with different strains of P. acnes for 3 hours to assess antibacterial activity. Bacteria was then enumerated by colony-forming unit assay to determine concentration, which was plotted as a percentage of untreated sample. 8 clinical isolates were tested, and the most and least susceptible to chitosan are displayed along with strain ATCC 6919. Error bars represent SEM (n = 3, independent experiments). **p < 0.01 (paired t-test).