Fluorescence microscopic images of P. acnes upon incubation with a fluorescein-labeled GPPPQGGRPQ peptide. P. acnes was suspended in a phosphate buffer containing 1.1 mM NaH₂PO₄, 1 mM NaH₂PO₄, and 100 mM NaCl, pH 6.5, and incubated with GPPPQGGRPQ (10 μM) (A), fluorescein-labeled CGKRK (10 μM) (B), or fluorescein-labeled GPPPQGGRPQ (1 μM [C] and 10 μM [D and E]) for 1 h at 37°C under anaerobic conditions. Incubation of fluorescein-labeled CGKRK was performed to exclude nonspecific binding. (F) P. gingivalis incubated with fluorescein-labeled GPPPQGGRPQ (10 μM). The green fluorescence (arrows) indicated that fluorescein-labeled peptide bound to P. acnes. (E) The green fluorescence was entirely quenched when a high concentration (1 mM) of unlabeled GPPPQGGRPQ was added to the incubation of fluorescein-labeled peptide (1 μM) with bacteria. Bar, 1 μm.

The GPPPQGGRPQ peptide suppresses the growth of P. acnes. P. acnes (1 × 10⁵ CFU) was incubated with PBS (A), antibiotics (B), and GPPPQGGRPQ at final concentrations of 1 μM (C), 10 μM (D), and 100 μM (E) for 3 h. After a 2-day incubation, bacteria were spotted on agar plates for colonization. Bacteria incubated with peptide were spotted in duplicate (C to E). (F) The activity of the GPPPQGGRPQ peptide in bacterial growth was determined by plating serial dilutions (10⁴ to 10⁷) of bacteria on agar plates and quantifying the CFU. Bar, 0.5 mm. The bars represent means ± standard errors for three separate experiments. The numbers of P. acnes bacteria treated with antibiotics (hatched bar) and peptide (solid bars) were compared with that of P. acnes treated with PBS (open bar). Student's t test was conducted for comparison. P values of <0.01 (*) and <0.005 (**) were considered significant.