Total Polyphenolic Content in S. aureus

The total polyphenolic content (TPC) in S. aureus Newman cultures was determined using Folin-Ciocalteu reaction according to Łopusiewicz et al. [43 (link)] with slight modification. 20 μL of suspension (1A–C) was mixed with 1.5 mL of deionized water and 100 μL of the Folin-Ciocalteu reagent (Sigma-Aldrich, Darmstadt, Germany), stirred gently for 5 min and mixed with 300 μL of a saturated solution of sodium carbonate (Sigma-Aldrich, Darmstadt, Germany). The mixture was allowed to stand in darkness for 30 min at 40 °C, followed by an absorbance reading at 765 nm using a spectrophotometer (Evolution 220 UV-Visible spectrophotometer, Thermo Fisher Scientific Inc., Waltham, DE, USA). A calibration curve of gallic acid (Sigma-Aldrich, Germany) in water:methanol (1:1, v:v) (0, 50, 100, 200, 400 and 500 μg/mL) was prepared and TPC was calculated as milligrams of gallic acid equivalents (GAE)/gram of S. aureus cell dry mass (mg GAE/g DM). Experiments were performed in triplicate.