Within the Gram stain procedure, which particular step plays the critical role in differentiating between gram-positive and gram-negative cells?

Question

BlackTom AI · Accepted Answer

To tackle this question, I’ll walk through how each step in the Gram stain contributes to distinguishing Gram-positive from Gram-negative cells.
Option a: alcohol (decolouriser). This step is the key differentiator. After the crystal violet-iodine complex has formed inside both cell types, the alcohol decolorises the cells differently: Gram-positive cell walls, with thick peptidoglycan, retain the CV-I complex and remain purple, whereas Gram-negative cell walls, with thinner peptidoglycan and an outer membrane, lose the dye and become colorless. This differential decolorization is what creates the contrast.
Option b: crystal violet (primary stain). The crystal violet stain initially colors both Gram-positive and Gram-negative cells purple. It is essential for staining, but it does not distinguish between the cell types by itself; without the subsequent decolorization step, both would appear the same. So while crucial, it is not the differentiating step.
Option c: iodine (mordant). Iodine forms a more stable CV-I complex within the cells, helping to trap the stain inside during the initial staining and in the immediate aftermath. It amplifies the color that results from the initial staining but does not by itself provide the differential outcome between Gram-positive and Gram-negative cells.
Option d: safranin (counterstain). Safranin is applied after decolorization to recolor the decolorized Gram-negative cells, rendering them pink/red. It does not drive the primary separation between the two groups; it merely provides contrast after decolorization has already occurred.

Within the Gram stain procedure, which particular step plays the critical role in differentiating between gram-positive and gram-negative cells?单项选择题

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