4 StainingPositively charged dye molecules are attracted to the negatively charged cytoplasmNegatively charged dye molecules are repelled by the negatively charged cytoplasm
5 Simple Staining Only one color used Crystal violet dye is positively charged, which is attracted by bacteria cytoplasm
6 Negative Staining A negatively charged dye is used What effect will this have on the bacteria cytoplasm?The cytoplasm will repel the dyeThe background will be stained, but not the bacteria cellLooks like the night sky
7 Heat Fixing Cells need to be adhered to the slide using heat Like an egg frying on a panAs proteins are heated, they denature and stick to the surfaceWe will heat the slides for 2-3 minutes on a hot plate
8 Gram StainingGram staining involves a series of staining steps used to differentiate between 2 types of bacteria cellsGram positive cells – stain blueGram negative cells – stain red
9 Gram Staining Steps Add crystal violet dye (wait 1 minute) Wash slide with waterAdd Gram’s iodine to lock in stain (wait 1 minute)Add alcohol decolorizer to remove stain from Gram negative cellsAdd safranin dye (wait 1 minute)
10 Warm-Up What is the purpose of staining cells? How do stains work? What is the purpose of Gram staining?What 2 dyes are used in Gram staining?What are the steps of Gram staining?
13 Bacterial Cells Ideal age for Gram staining bacteria cells is 24 hours Gram positive bacteria are susceptible to certain antibiotics (like penicillin)Gram negative bacteria are susceptible to other types of antibiotics