Gram Staining

differential stain -very useful for identifying and classifying bacteria as either gram negative or gram positive. -primary stain -mordant -decolorizing agent secondary stain or counterstain

crystal violet. -all bacteria are stained purple by this basic dye

gram's iodine iodine combines with crystal violet in the cell to form a crystal violet-iondine complex

ethyl alcohol or ethyl alcohol-acetone primary stain is washed of some bacteria while others are unaffected

or counterstain (safranin) this basic dye stains the decolorized bacteria red

those that decolorize easily -pink E. coli

those that retain the primary stain and do not decolorize easily -purple bacillus S. epidermis

bacteria stain differently in their cell walls gram stain is most consistent when done on young cultures of bacteria because the gram stain is usually the first step in indentifying the bacteria

old gram-positive cells stain gram-negative bcuz cell wall starts to deteriorate and takes in the color iondine cannot be added before primary stain bcuz it is not a stain itself but it attaches to crystal violet -safaranin can be ommitted bcuz if gram + still purple, gram - will be colors less , so u can still tell the difference gram positive and gram negative differ for antibiotics