Propidium ion enters viable cells with high membrane potential during live-dead staining

- Re-examination of the widely used live-dead staining method
- Showing that cells with a high membrane potential take up propidium ions like dead cells
- Explaining the uptake with the electrochemical properties of the propidium ion

Live-dead staining with propidium iodide can give erroneous results for bacteria showing high membrane potentials. We observed uptake of propidium ions across intact cell membranes for Dinoroseobacter shibae and Bacillus subtilis. Apparently, a high membrane potential facilitates breakthrough of the double-charged propidium ion and can mark viable cells as dead.