Can Iodine be added before the primary stain in a graim stain?

Answer 1

Iodine is not a stain; it is a mordant. It doesn't give color directly to the bacteria but it fixes the crystal violet ( primary stain)to the bacterial cell wall.

Crystal violet (CV) dissociates in aqueous solutions into CV+ and chloride (Cl-) ions. These ions penetrate through the cell wall and cell membrane of both Gram-positive and Gram-negative cells. The CV+ ion interacts with negatively charged components of bacterial cells and stains the cells purple. Iodine (I- or I3-) interacts with CV+ and forms large complexes of crystal violet and iodine (CV–I) within the inner and outer layers of the cell.