title: Rapid fluorometric quantification of bacterial cells using Redsafe nucleic acid stain.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Clinical Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Khalili
authors.affiliation: Department of Clinical Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Vahid
authors.initials: V
authors.lastname: Hosseini
authors.affiliation: Department of Clinical Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Roya
authors.initials: R
authors.lastname: Solhi
authors.affiliation: Department of Clinical Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran; Recombinant Vaccine Research Center, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Aminian
keywords: Bacterial enumeration; MTT assay; Redsafe; fluorometric assay