Bacteria are first exposed to growth medium and grow in the narrow grooves. Ampicillin treatment (marked "Amp") results in the massive lysis of cells. After the ampicillin is washed out, persister cells grow and divide. Note that the persister cells were are slowly growing before, during and after the ampicillin treatment. Time between consecutive frames: 4 minutes during the first growth medium period and the first two hours of the ampicillin treatment; 11 minutes during the end of the ampicillin treatment and the second growth period.