Fig. 1.

Cephalexin treatment followed by filtration enables highly efficient enrichment of antibiotic-tolerant cells. a Susceptible, exponential phase cells filament severely during treatment with cephalexin (50 µg/ml) before lysis occurs (scale bar: 20 µm). b Experimental set-up of our persister enrichment method. A culture in exponential phase is treated with cephalexin for 1 h to induce filamentation of susceptible cells. Next, the culture is vacuum filtered (pore size of 5 µm) to separate short, antibiotic-tolerant persisters from filamented, susceptible cells. After filtration, the culture is centrifuged to remove cephalexin and to increase the density of the resulting sample. c Microscopic visualization of a sample after cephalexin treatment and filtration demonstrates that it mainly consists of short cells that did not respond to the cephalexin treatment (scale bar: 20 µm). d Side scatter distributions of a sample before and after filtration confirm that filtration enriches for cells with the lowest side scatter values, presumably corresponding to the persisters of the culture (SSC: side scatter).