Two viability substrates, ChemChrome B and 5-cyano-2,3,4-tolyl-tetrazolium chloride (CTC) were compared with the traditional pour plate method for the enumeration of bacteria in potable water samples. ChemChrome B stained cells were counted, on a membrane, using a novel laser scanning device whereas CTC stained cells were counted using epifluorescence microscopy. A significantly higher number of bacteria were detected using the viability assays than by culture, which highlights the inefficiency of current culture techniques. Results with ChemChrome B illustrate that the use of a laser scanning device provides an efficient method for the enumeration of fluorescently labelled microorganisms.

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