Evaluation of ChemChrome V6 for bacterial viability assessment in waters

The efficiency of ChemChrome B (CB) and ChemChrome V6 (CV6) dyes to stain v iable bacterial cells in water was compared. Both dyes are fluorogenic este rs converted to free fluorescein by esterase activity. The dyes were applie d to a wide variety of bacterial species, including those poorly stained by CB, and to natural waters. Some species tested gave unacceptable low fluor escence intensities by being inefficiently or non-labelled with the CB. In contrast, CV6-stained bacteria were easily detected by both flow cytometry and solid-phase cytometry. As a consequence, higher viable cell counts were found with CV6 compared with CB in natural waters. Viable counts determine d by CV6 staining were always higher than cfu counts. In constrast, respiri ng cell counts (CTC) were always lower than CV6 counts and, in the case of tap and mineral waters, they were lower than cfu counts.