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 enumer- ation 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 colou- rimetric assay for enumeration of bacterial cells. results: obtained results showed that fluorometric assay threshold for lb grown e. coli is 6×104  cfu/ml. redsafe fluo- rescent 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.