Bacterial cultures of EPEC or E. coli K-12 were grown overnight in LB media (Non-Activation) or in DMEM for 3 hr at 37°C to OD600 ~0.3 (Activation). Cultures were then diluted, plated on LB agar, and incubated at 32°C (non-activating conditions). Colony appearance time was monitored by ScanLag at 15 min intervals. The resulting histograms show (A, B, C, D) the fractions of colonies detected at each time point and (E, F) colony size distributions 1000 min after plating. Colonies larger or smaller than 105 pixels were defined as ‘BIG’ and ‘SMALL’ morphotypes, respectively. (A–C, E, F) Experiments were repeated in at least four independent biological replicates. (D) shows the cumulative of 4 independent biological replicates. (G) Time-lapse microscopy phase-contrast images of the two co-existing morphotypes, BIG and SMALL. Time points are indicated. Similar results were obtained in at least 10 different locations and in two independent biological replicates. Scale bar: 50 μm.