GRAM STAINING : Mechanism , Limitations and Modified techniques
GRAM STAINING: Mechanism , Limitations and Modified techniques Gram stain or Gram staining, also called Gram’s method, is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique. Gram staining differentiates bacteria by the chemical and physical properties of their cell walls. Gram-positive cells have a thick layer of peptidoglycan in the cell wall that retains the primary stain, crystal violet. Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out with the addition of ethanol. They are stained pink or red by the counterstain, commonly safranin or fuchsine. Lugol’s iodine solution is always added after the addition of crystal violet to strengthen the bonds of the stain with the cell membrane. Gram staining is almost always the first step in the preliminary identification o