BIOL240 Lecture Notes - Lecture 8: Alcian Blue Stain, Crystal Violet, Negative Stain
Document Summary
Cell wall of certain species is surrounded by capsule, slime layer, or glycocalyx (consists of polysaccharides, polypeptides and/or carbohydrate material giving structure an enlarged appearance. Alcian blue (basic dye that is water-soluble in nature) forms linkages with the acid groups of acidic muecpolysaccharides staining them blue. Disease-producing bacteria -> heavy capsule means highly virulent form of the organism (presence of capsule makes destruction of microbe by phagocytic cells more difficult) Capsule may also be detected using negative stain -> unstained halo-like material surround cells would represent the capsule. Polysaccharides are water soluble and uncharged so simple stains will not adhere. Capsule-staining stains the bacteria and the background leaving capsules unstained (essential. Pipette a drop of nigrosin near one end, then a drop of organism. Flood with tap water until runs off edge then tip the water, continue until water is clear (floating the crystal violet prevents it from forming a precipitate and sticking to the slide)
