BIOL240L Study Guide - Final Guide: Gram Staining, Methylene Blue, Enterobacter Aerogenes
11 Dec 2016
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Color compound stain used to increase the contrast bw the specimen and the background. Simple staining procedure: single stain is used, all cells and structures generally stain the same colour, distinguish bacterial cells of various morphological types. Cocci, rods, spirals, vibrios: dyes used: methylene blue(blue), basic fuchsin(red), crystal violet(purple) Positive staining procedures: stain basic, positively charged (cationic) chromo (=colour) phore. Bacteria are slightly negatively charged on their outer surface: attraction between these cationic chromophores and the organism. Methylene blue stain has blue chromophore, resulting in positive blue staining of the organism. Sterilization of inoculating loop: hold loop like a pencil, flame the loop first in cool part (yellow) then hot (blue) until it turns red, 45 degree angle. Heat fixing a slide: quickly pass the slide with smear side face up through bunsen burner flame 2-3times, prevents bacteria from washing away when stained by coagulating proteins and fixing them to the slide. Magnification achieved by a compound microscope by: objective.
