Rapid fluorometric quantification of bacterial cells using Redsafe nucleic acid stain.

BACKGROUND AND OBJECTIVES Numerous procedures in biology and medicine require the counting of cells. Direct enumeration of Colony Forming Units (CFUs) is time-consuming and dreary accurate cell counting on plates with high numbers of CFUs is error prone. In this study we report a new indirect cell counting method that was developed based on the use of Redsafe fluorometric assay. The usefulness of Redsafe, a nucleic acid stain, in liquid medium is based on the binding of the fluorescent dye to DNA. MATERIALS AND METHODS Redsafe fluorometric assay was evaluated in comparison with MTT colorimetric assay as a colourimetric assay for enumeration of bacterial cells. RESULTS Obtained results showed that fluorometric assay threshold for LB grown E. coli is 6×10(4) CFU/ml. Redsafe fluorescent assay can be used as a rapid and inexpensive method for bacterial enumeration and quantification with increased sensitivity. CONCLUSION The sensitivity of the Redsafe fluorometric assay for detection and enumeration of bacterial cells was 2-log-unit more than that was observed for the MTT assay.