Effect of nutritional environment on antibiotic tolerance of wild-type E. coli biofilm cultures. Cells were grown as biofilms for 6 hours before being transferred to treatment plates for 24 hours. All cultures were grown at 37°C in LB medium with or without an additional carbon source. All carbon source supplements were added at 10 g/L, the succinic acid solution was pH adjusted to 6.8 before being added to medium. Reported cfu/biofilm data was determined after treatment. 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.