Quantitative Analysis of the Gram Reaction

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Abstract
SUMMARY: The crystal violet and iodine uptake by suspensions of Staphylococcus aurcus and Escherichia coli was determined. It was found that equal amounts of intracellular dye-iodine complex were formed in these micro-organisms. The molar ratio dye to iodine was 1:2. The extractability of this complex with methanol and ethanol was compared with the relative solubility of dye-iodine precipitates. Results with E. coli suggest that the solvents pass freely into the cells and decolorize them after dissociation of the dye-iodine complex. Gram-positive micro-organisms may be arranged in a number of groups according to their extractability pattern with regard to the complex. These patterns suggest the presence of interaction between the cells and ethanol. This interaction may be located at the cell wall.