INFLUENCE OF PHOSPHATE BUFFER ON CRYSTAL VIOLET UPTAKE AND RETENTION BY BACTERIAL CELLS AS RELATED TO THE GRAM REACTION

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Abstract
Quantitative determinations showed that crystal violet uptake by Sarcina lutea reaches a greater maximum in non-buffered solutions than in the presence of M/15 phosphate buffer pH 7.1. When stained cells are washed with buffer, the buffer acts as a decolorizer and removes dye from the cells. Crystal violet is removed in this manner both before and after stained cells are exposed to iodine. Determinations of dye-binding capacity of bacterial cells made in the presence of phosphate buffer followed by buffer washes of the stained cells represent more correctly the amount of dye retained by cells rather than dye adsorbed or dye taken up. Failure to recognize these differences has led to claims that capacity for adsorption of crystal violet may be correlated with the gram characteristic. When crystal violet uptake is determined in the absence of buffer or buffer washes, no such correlation exists.

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