Effect of culturing phase on antibiotic tolerance of wild-type E. coli K-12 cultures. Cells were grown as biofilms for 6, 12, or 24 hours prior to being transferred to treatment plates. Cultures treated after 6 hours were in late exponential phase while the 12 and 24 hour samples were in stationary phase. Reported cfu/biofilm data was determined after treatment. Cultures were grown at 37°C. 8a) LB only medium. 8b) LB and 10 g/L glucose. Black bars = control, dark gray bars = kanamycin (100 ug/ml) challenge, light gray bars = ampicillin (100 ug/ml) challenge. Number at the base of each bar denotes the number of independent replicates. cfu = colony forming unit.