QUANTITATIVE STUDIES OF DIFFERENTIAL STAINING REACTIONS I

Abstract

The isoelectric zone of Escherichia coli as determined by the dye method can be made quantitative by micro-Kjeldahl analyses of stained cells and of staining and buffer solutions. The values obtained are relative rather than absolute. The amount of crystal violet retained per mg of bacterial nitrogen in Micrococcus pyogenes var. aureus was greater than that retained by Escherichia coli when the pH of the staining solution was 7.5. This relationship was reversed when the pH of the staining solution was 5.2. M. pyogenes var. aureus and E. coli retained less dye when stained in the absence of M/15 phosphate buffer at pH 7.1 than they retained in the presence of buffer. Phosphate buffer will serve as a decolorizer of stained cells but the decolorizing capacity is minimal at a pH of about 7.0. The quantity of acid-fuchsin retained by E. coli can be measured by micro-Kjeldahl analyses. Staphylococci retained less than 0.02 mg of acid-fuchsin nitrogen per mg of bacterial nitrogen.