Description
Gram’s iodine, also known as Lugol’s solution, is a crucial component of the Gram staining technique used in microbiology laboratories. It is a brownish-orange solution consisting of iodine and potassium iodide dissolved in water. Gram’s iodine serves as a mordant in Gram staining, enhancing the binding of the primary stain (crystal violet) to the bacterial cells.
During the Gram staining process, Gram’s iodine is applied after the bacterial cells have been stained with crystal violet. The iodine solution forms a complex with the crystal violet dye, trapping it within the thick peptidoglycan layer of Gram-positive bacterial cell walls. This complex prevents the removal of the crystal violet stain during the subsequent decolorization step.
Gram’s iodine plays a crucial role in differentiating between Gram-positive and Gram-negative bacteria by stabilizing the crystal violet-iodine complex in Gram-positive bacteria. As a result, Gram-positive bacteria retain the purple color after the decolorization step, while Gram-negative bacteria lose the stain and are subsequently counterstained with safranin.
In addition to its role in Gram staining, Lugol’s solution has various other applications in medicine, veterinary science, and histology. It is used as an antiseptic for wound treatment, as a staining agent for microscopy, and as a diagnostic tool for detecting starch in biological samples.