C. acnes KCCM 41747 (ATCC 6919) (isolated from human facial acne), methicillin-sensitive S. aureus ATCC 6538, and fluconazole-resistant C. albicans strain DAY185 were used in this study. The C. acnes strain was cultured on Reinforced Clostridium Media (RCM)-agar plates for colony preparation and in liquid RCM at 37°C under anaerobic conditions (BD GasPak EZ Gas Generating Anaerobic Pouch Systems; Fisher Scientific, Pittsburgh, PA, USA) for all other experiments. The S. aureus strain was cultured in LB medium at 37°C, and the C. albicans strain was cultured in Potato Dextrose Broth (PDB) medium at 37°C.
Twenty indoles, namely, 7-azaindole, 7-benzyloxyindole, 3,3′-diindolylmethane (DIM), 7-formylindole, 7-hydroxyindole, indole, indole-3-acetamide, indole-3-acetic acid, indole-3-acetonitrile, indole-3-butyric acid, indole-3-carbinol, indole-3-carboxyaldehyde, indole-7-carboxylic acid, indole-3-propionic acid, isatin, 7-methoxyindole, 7-methylindole, methyl indole-7-carboxylate, 7-nitroindole, and 2-oxindole were purchased from Sigma-Aldrich (St. Louis, MO, USA), Wako Chemicals Inc. (Richmond, VA, USA) or Combi-Blocks, Inc. (San Diego, CA, USA). Dimethyl sulfoxide (DMSO) was used to dissolve all indoles, and 0.1% (vol/vol) DMSO was used as the negative control; at this concentration, DMSO did not affect bacterial growth or biofilm formation.
Twenty indoles, namely, 7-azaindole, 7-benzyloxyindole, 3,3′-diindolylmethane (DIM), 7-formylindole, 7-hydroxyindole, indole, indole-3-acetamide, indole-3-acetic acid, indole-3-acetonitrile, indole-3-butyric acid, indole-3-carbinol, indole-3-carboxyaldehyde, indole-7-carboxylic acid, indole-3-propionic acid, isatin, 7-methoxyindole, 7-methylindole, methyl indole-7-carboxylate, 7-nitroindole, and 2-oxindole were purchased from Sigma-Aldrich (St. Louis, MO, USA), Wako Chemicals Inc. (Richmond, VA, USA) or Combi-Blocks, Inc. (San Diego, CA, USA). Dimethyl sulfoxide (DMSO) was used to dissolve all indoles, and 0.1% (vol/vol) DMSO was used as the negative control; at this concentration, DMSO did not affect bacterial growth or biofilm formation.