QUANTITATIVE STUDIES OF DIFFERENTIAL STAINING REACTIONS II

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Abstract
Quantitative determinations of the adsorption and retention of dye by bacteria were made by means of a micro-Kjeldahl procedure. The degree of Gram-positivity can be altered by means of chemical treatment of the cells before staining. Escherichia coli increased in Gram-positivity after treatment with crystal violet, sodium bisulfite and NaOH. Micrococcus pyogenes var. aureus decreased in Gram-positivity after treatment with picric acid. The omission of Gram''s iodine from the staining procedure in converted E. coli resulted in complete removal of crystal violet by decolorization as judged by micro-Kjeldahl analyses. Microscopically, crystal violet was still retained when iodine was omitted from the procedure. The counterstain, safranin, was capable of replacing or masking the residual crystal violet. Fixation of Gram-positive cells with formalin (pH 7.1) markedly reduced the amount of crystal violet retained. Living (unfixed) cells of M. pyogenes var. aureus were Gram-negative or markedly less Gram-positive and adsorbed less dye than did fixed cells. Unfixed cells of E. coli showed a decrease in dye adsorption and an increase in dye retention.

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