Question

In Gram stain if at the end of the procedure both the -positive and Gram-negative bacteria appear red what was the most common technical error made?

Answer 1

In the procedure of gram staining, we know that the steps are

1. Taking the bacteria and make a smear of it,

2, Heat fix on the slide,

3. Application of crystal violet (primary stain),

4. Application of iodine (mordant),

5. Alcohol wash (Decolurisation),

6. Application of safranin (counterstain).

If the process if we apply the primary stain, we put the iodine as a mordant which helps the color to remain in the gram-positive bacterial cell wall. After the decolorization process is done, gram-negative bacteria will lose their cell wall and take up the counterstain color. Thus, the main technical fault here made the absence of the mordant (iodine) application.