Decreased sensitivity to norfloxacin from addition of adenine BW27784 was grown overnight in RM minimal medium with 0.2% glycerol and then diluted 1:100 and grown to exponential phase. (a) The exponential phase culture was diluted twofold with RM medium with (o) no addition, (+) 250 μg/ml adenine, (Δ)120 ng/ml norfloxacin, or (◊)120 ng/ml norfloxacin and 250 μg/ml adenine. Absorbance was measured at 37°C every 20 min using the Perkin Elmer 7000 Plus BioAssay Reader with the filter set at 590 nm and shaking for 10 min before each measurement. (b) Exponential phase culture was treated with 200 ng/ml norfloxacin with or without 250 μg/ml adenine along with controls with no treatment or adenine alone. After 3 h at 37°C, viable colony counts were determined by dilution and plating on LB plates.