Can gram-negative bacteria be stained with Crystal Violet?

Question

Logan Allen · Accepted Answer

No, only gram-positive bacteria can be stained with Crystal violet.

Crystal Violet is used as a dye to stain bacteria to understand the strain, this process is called Gram staining. Gram staining is completely based on the characteristic of bacteria either to retain Crytal violet or not.

Gram-positive bacteria can retain the crystal violet dye even after washing with alcohol due to peptidoglycan layer surrounding the bacteria. Whereas, Gram-negative bacteria cannot retain the crystal violet dye after washing with alcohol due to the absence of peptidoglycan layer.

There are few Bacteria which are not related to Gram-positive but still do retain crystal violet, these bacterias can be distinguished using specialized staining.

Figure 1 A Gram stain of mixed Staphylococcus aureus (S. aureus ATCC 25923, gram-positive cocci, in purple) and Escherichia coli (E. coli ATCC 11775, gram-negative bacilli, in red).

Julian Aguilar · Answer

undefined Gram-negative bacteria cannot be stained with Crystal Violet alone because their cell walls contain an outer membrane that prevents the Crystal Violet from penetrating. However, they can be stained using a technique called the Gram staining method, where they are first stained with Crystal Violet, then treated with a decolorizing agent, and finally counterstained with a contrasting dye such as safranin.