Bacteria are ubiquitous in oceans, lakes and ground, where they constitute an important component of the ecosystem biomass. The major problem is to count the number of bacterial cells and measure the funcional characteristic of individuals. Most bacteria obtained from field samples are difficult or impossible to grow in traditional culture media. Epifluorescence microscopy is tedious and time consuming in order to obtain a precise estimation of bacteria abundance and viability.

In the present study, flow cytometry was used to characterize bacterial cells from diverse origins: one strain of E.Coli and samples obtained from sewage disposal system. The use of a high sensitivity flow cytometry (Bio-Rad Bryte-HS) and DAPI/PI double staining, allowed the rapid measurement of important parameters in bacterial samples:

1) total cell number, with the detection od DAPI or PI (after permeabilization) fluorescent cells; 2) percentage of viable cells after DAPI/PI double staining; 3) cell biovolume after forward light scatter signal normalization with reference standard beads

The comparasion of the flow cytometry results with the reference methods (epifluorescence microscopy and traditional culture media) indicates that this analytical protocol offers a reliable and fast method for a real time multiparametric analysis in the bacterial ecology field.