Assessment of the effects of gramicidin, formaldehyde, and surfactants on Escherichia coli by flow cytometry using nucleic acid and membrane potential dyes.

Two membrane potential sensitive dyes (Rhodamine 123 and bis-oxonol) and three nucleic acid dyes (propidium iodide, SYTO-13, and SYTO-17) were used to assess the effect of surfactants on Escherichia coli. The ability of E. coli to be stained by these probes was validated at different physiological states. Propidium iodide was used to assess the integrity of cell envelopes. Two double staining methods based on propidium iodide with SYTO-13 and bis-oxonol with SYTO-17 were used to improve the discrimination between bacteria and micelles or aggregated particles generated by the presence of surfactants. A rapid (1 h contact time between cells and surfactants, and less than 5 min for staining and obtaining data) Rhodamine 123 flow cytometric assay was developed to assess the bactericidal effect of surfactants.