it is important that microbiologists can correctly identify bacteria that can cause infections to enable them to decide the most effective treatment
during the staining technique, two stains are added to the bacterial smear
crystal violet and safranin
1
application of crystal violet (purple dye)
2
application of iodine (mordant)
3
alcohol wash added (decolorization)
4
application of safranin (counterstain)
gram positive
see a purple stain when observing the smear under a microscope it shows gram positive bacteria
gram negative
smear has retained pink safranin stain, shows gram negative bacteria are present
gram negative
this is because their thinner cell walls and lipid membranes allow ethanol to wash off all the crystal violet stain and to then retain pink safranin stain
