BIOL240 Study Guide - Final Guide: Staphylococcus Epidermidis, Gram Staining, Crystal Violet
4 Dec 2013
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Colour compound stain used to increase contrast between specimen and the background. Simple staining procedure (using a single stain) Methylene blue (blue), basic fuchsin (red), crystal violet (purple) Positive: stain is basic, positively charged (cationic) and the slightly negative charge on the bacteria attracts the stain. Resolving power is the ability to distinguish between two images as separate (0. 2 um is best for this microscope) Rod (bacillus), round (coccus) and spiral (spirillium) Stalked forms (caulobacter), club-shaped (corynebacterium) and comma shaped (vibrio) Magnification = size of specimen in drawing / estimated or actual size. Gram stain used to differentiate between types of bacteria. Stain fix smear with primary stain (crystal violet), then add gram"s iodine which acts like a mordant (fixes primary stain to cells), then wash with a decolourizing agent (95% ethyl alcohol), then a counterstain (safranin) Gram-positive organisms will not be easily decolourized and will be purple (crystal violet) Gram-negative organisms will be decolourized and will appear red (safranin)
