FIG 1.

Qualitative assay to identify potential antibiotic-Fe³⁺ complexes. Binding of iron by a compound causes spectral shifts that can be detected visually. Five microliters of stock concentration antibiotic (listed below) was added to 5 μl of FeCl₃ to a final FeCl₃ concentration of 10 μM and incubated at room temperature for 1 h. Negative controls without iron are indicated by a minus sign and droplets with FeCl₃ are indicated with a plus sign. Vehicle controls with Milli-Q H₂O and DMSO were included. The concentrations of each antibiotic stock were as follows: TOB (tobramycin; 4 mg/ml), GENT (gentamicin; 10 mg/ml), DSX (deferasirox; 20 mg/ml), DFP (deferiprone; 60 mg/ml), OFL (ofloxacin; 4 mg/ml), PPA (pipemidic acid; 64 mg/ml), CIP (ciprofloxacin; 5 mg/ml), DOXY (doxycycline; 50 mg/ml), TET (tetracycline; 20 mg/ml), MIN (minocycline; 20 mg/ml), CAR (carbenicillin; 100 mg/ml), PIP (piperacillin; 6 mg/ml), CEFU (cefuroxime; 30 mg/ml), CEFO (cefotaxime; 30 mg/ml), AMP (ampicillin; 30 mg/ml), CLOX (cloxacillin; 30 mg/ml), MEC (amdinocillin; 30 mg/ml), CEFT (ceftriaxone; 30 mg/ml), CEFIX (cefixime; 12 mg/ml), VAN (vancomycin; 30 mg/ml), TS (thiostrepton; 20 mg/ml), CHLOR (chloramphenicol; 50 mg/ml), POLY (polymyxin B; 4 mg/ml), and TRI (trimethoprim; 50 mg/ml).