gram staining

• 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