Comparison of planktonic and biofilm antibiotic tolerance. Wild-type E. coli K-12 cultures were grown on LB only medium at 37°C. Cultures were grown for 6 hours before being transferred to fresh antibiotic treatment medium for 24 hours. Reported cfu/ml and cfu/biofilm data was determined after treatment. Black bars = control, dark gray bars = kanamycin (100 ug/ml), 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.