Lb medium

The IPTG/X-gal stock solution: 1.25 g IPTG (Sigma–Aldrich, St. Louis, MO) and 1 g X-gal in 25 mL DMSO (Sigma–Aldrich, St. Louis, MO). Tetracycline (Sigma–Aldrich, St. Louis, MO) stock suspension: 20 mg/mL Tetracycline in 1 mL of 96% ethanol. LB/IPTG/X-gal plates: 1 L LB medium (AppliChem GmbH, Darmstadt, Germany), 15 g/L agar, and 1 mL IPTG/X-gal stock solution. LB/Tet plates: 1 L LB medium, 15 g/L agar and 1 mL Tetracycline stock (15 mg/mL). PEG/NaCl: 20% (w/v) PEG 8000 (Sigma–Aldrich, St. Louis, MO), 2.5 M NaCl. Iodide buffer: 10 mM Tris-HCl (pH = 8), 1 mM EDTA and 4 M NaI (Sigma–Aldrich, St. Louis, MO).

The antimicrobial activity of the eluted released gentamicin was determined using an agar diffusion test regime with a Gram-positive bacterium, Staphylococcus aureus, clinically isolated, as described before [13 (link)]. Bacteria were grown in a LB medium (2 g yeast extract, 4 g tryptone (both Applichem GmbH Darmstadt, Germany, 2 g NaCl (Sigma-Aldrich, Darmstadt, Germany) and 400 mL H₂O double dest)) and plated on LB agar plates (LB medium containing 1.5% (w/v) agar (Applichem GmbH, Darmstadt, Germany)) to get a bacterial lawn. Fifty µL of the eluate were pipetted on filter discs (diameter = 12 mm), which were placed in the middle of the agar gel. After 24 h of cultivation at 37 °C, the extent of the inhibition zones was measured.