BIOL 2053 Lecture Notes - Lecture 29: Gram Staining, Crystal Violet, Gram-Negative Bacteria
27 Nov 2018
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Colony morphology used to describe the appearance of colonies that have been cultured on solid media. Distinguishing colony morphology is important when attempting to isolate pure cultures. Plates with fewer than 30 colonies give too statistically unreliable results and plates with more than 300 colonies are too crowded to form distinct colonies. Multiple your colony count by the dilution factor on the plate. Add a small drop of water onto a slide and mix a colony into this using a sterile loop to create a hazy smear. Heat fix once dried by passing the slide through the flame 3 times to heat fix. Gram positive cells have a thick peptidoglycan layer that absorbs the pigments in gram staining: cover with crystal violet. This stains all cells purple: wash with water, cover with gram"s iodine. This intensifies the stains: wash with water, cover with acetone alcohol.
