Validation of flow cytometry for rapid enumeration of bacterial concentrations in pure cultures

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Abstract
Flow cytometry was investigated as a rapid detection and counting method for bacteria in pure cultures. A simple two-parameter detection scheme was employed: particle size was measured by forward angle light scatter and nucleic acid content by fluorescence of the DNA/RNA-binding dye ethidium bromide. The technique gave results that correlated exceptionally well with conventional plate counting for four species of bacteria, and concentrations in the range of 102 to 107 cfu/ml. Cytometric counts were obtained in a few minutes, as compared with 2 d required for the plate counts. Under ideal conditions, each bacterial species examined exhibited a characteristic ''signature; on the cytometer, which could be explained by its known properties and morphology.