Direct Count of Bacteria Using Fluorescent Dyes: Application to Assessment of Electrochemical Disinfection

A rapid method for direct counting of viable and dead cells using two fluorescent dyes, propidium iodide and 4 ', 6-diamidino-2-phenylindole, was developed for estimation of cell viability after electrochemical disinfection. Using this double staining method, dead and viable cells were visualized as red and blue fluorescent cells, respectively, under UV excitation employing epifluorescence microscopy. A good correlation between the red cell ratio and the ratio of dead cells determined by the plate count method was obtained for Vibrio alginolyticus cells exposed to heat (60 °C), 10 ppm of chlorine, 3.7% of formaldehyde, and electrochemical disinfection treatment.