The synthesis of tricyclic flavonoid BrCl-flav has been described in detail in our previous report [59 (link)]. NMR, MS, IR and elemental analysis were used to determine the structure and purity (>99%) of the final compound. The stability of BrCl-flav towards Mueller–Hinton broth (Scharlau, Barcelona, Spain) and phosphate buffer saline (PBS) was monitored by UV–Vis spectroscopy. The tricyclic flavonoid was stable during the performed antimicrobial tests.
The antibiotics used in this study were purchased from local suppliers (Carl Roth and Sigma-Aldrich, Darmstadt, Germany, Scharlau, Barcelona, Spain); chloramphenicol and gentamicin were used as reference antibiotics for minimum inhibitory concentration assays, while ciprofloxacin, penicillin and tetracycline were used for combination tests; different antibiotics (Oxoid, Basingstoke, UK) were used for the antimicrobial susceptibility assay according to CLSI guidelines [60 ].
The antibiotics used in this study were purchased from local suppliers (Carl Roth and Sigma-Aldrich, Darmstadt, Germany, Scharlau, Barcelona, Spain); chloramphenicol and gentamicin were used as reference antibiotics for minimum inhibitory concentration assays, while ciprofloxacin, penicillin and tetracycline were used for combination tests; different antibiotics (Oxoid, Basingstoke, UK) were used for the antimicrobial susceptibility assay according to CLSI guidelines [60 ].