Antibiotic stocks Ampicillin (50 mg/ml) in water, filter sterilize, store in -20 °C. Working concentrations 20-125 mg/ml. Kanamycin (25mg/ml) in in water, filter sterilize, store in -20 °C. Working concentrations 10-50 mg/ml. Tetracycline (10 mg/ml) in 50% ethanol, store in dark -20 °C. Working concentrations 10-50 mg/ml. Chloramphenicol (25 mg/ml) in ethanol, store in -20 °C. Working concentrations 25-175 mg/ml. Streptomycin (10 mg/ml) in water, filter sterilize, store in -20 °C. Working concentrations 10-50 mg/ml. Carbencillin (50 mg/ml) in water, filter sterilize, store in -20 °C. Working concentrations 20-60 mg/ml. Hygromycin B (100 mg/ml) in water, filter sterilize, store in -20 °C. Working concentrations 50-100 mg/ml. 1:1000 dilution of the antibiotic stocks is frequently used for liquid media and 1:500 dilution is frequently used for agar plates.