BIOL240 Lecture Notes - Lecture 4: Staphylococcus Epidermidis, Crystal Violet, Escherichia Coli
Document Summary
Used to differentiate types of bacteria depending on their abilities to retain a particular stain (referred to as a differential staining technique) Fixed smear of organisms with a primary stain of crystal violet. Gram s iodine stain (known as mordant -> substance that fixes the primary stain in the bacterial cells. Wash stained smear with decolorizing agent (95% ethyl alcohol) Allow all stains to sit for 1 minute. Gram-positive organisms will not be easily decolourized, retain purple stain of crystal violet. Gram-negative organisms will be decolorized by the alcohol and will be stained by the safranin and appear red or pink. Think smears may take more time to decolorize. If smears are overheated during heat fix, the cell walls would rupture causing gram-positive cells to release primary stain and accept counter stain. Decolourization -> solution flows colourlessly, if left on smear too long some gram-positive cells may appear gram-negative. Excess water left on slide may dilute reagents.
