1. Allow DAPI solution a) to stand at room temperature for 30 minutes. Solution should be protected from light.
2. Resuspend the organisms with PBS(-) or saline and adjust the number of cells to 106cells/mL(flow cytometry) or 108-109cells/mL(microscopy).
3. Add 1 μL of DAPI solution into the microbial cell suspension and vortex gently to mix. Formaldehyde-fixation can be recommended if necessary.
4. Incubate the microbial cells at room temperature for 5 minutes.
5. Analyze the stained-cells by a flow cytometer or a microscope. The maximum wavelengths of the dye are 360 nm for excitation and 460 nm for emission.
a) Since DAPI may be carcinogenic, be careful when handling and disposing.
Fig. 2 L. casei stained with CTC and DAPI (left). B. cereus stained with CFDA and DAPI (right).