Abstract: A bacterial staining composition, process and apparatus for detection and quantitation of gram negative and gram positive bacteria in fluid samples are disclosed. The composition comprises a net negatively charged filter onto which bacteria are adsorbed and concentrated, an acid diluent which alters the electrostatic charge of the bacteria, thus enabling adsorption of the bacteria to the filter, a bacterial stain operative at about pH 8 to 12, and a washing reagent which enhances the diffusion of free dye away from the immobilized, stained bacterial. The color intensity at the center of the filter surface manifests the stained bacteria. It is compared to a standard color guide to determine the number of bacterial present in the fluid sample.