Antibiotic Susceptibility Testing of Cyanobacteria

Three classes of antibiotics: β-lactams (ampicillin, cefotaxime), aminoglycosides (kanamycin), and tetracycline, were tested in this study. Antibiotic stock solutions (25x–100x) were prepared according to the manufacturer’s instructions and stored at -20°C. Working solutions in the range of 0.2–102.5 mg/L for ampicillin, kanamycin, cefotaxime and 410 mg/L for tetracycline were used in this study (Dias et al., 2015 (link); Shang et al., 2015 (link)). Ampicillin, cefotaxime, and kanamycin working solutions were prepared immediately before use and diluted in ddH₂O to the desired concentrations (Baselga-Cervera et al., 2019 (link)). Each antibiotic concentration was mixed with 5 ml F. diplosiphon cells adjusted to OD750 nm. Assays were performed in 96-well clear polystyrene microplate (Corning^®Inc., NY) and cultures grown under conditions mentioned above. Three replicate treatments were maintained and the experiment was repeated twice. In order to minimize the effects of light scattering, every other well was left blank. Plates were sealed with a Breathe-Easy sealing membrane (Sigma-Aldrich, MO, Lot#MKCP8263) to prevent evaporative water loss and decrease the risk of contamination.