Counter Staining with Safranin?

Question

After Gram Staining,\nWe use counter staining to find out that is there any gram(-) bacteria present on the prepared slide.\n\nMy question is-\n\n**What component in the cell wall of gram(-) bacteria is responsible for the retention of Safranin dye?**\nLike the Techoic Acid is responsible for the retention of CVI complex in gram (+) bacteria. \n\nAs I have just studied the staining process,any additional useful information is appreciated. \n\nThanks!

Answer 1

Safranin actually coats both Gram + and Gram - bacteria. It is known to color all cell nuclei red.

Because at this step (counter staining), Gram + bacteria have a violet color, the red color from safranin is masked by the dark CVI stain.

The critical difference in gram stained bacteria is the presence or absence of techonic acid (just like you said). This determines whether or not CVI binds the bacteria and consequently whether or not safranin gets masked by CVI.

Gram - cells do not have techonic acid, therefore do not bind CVI and portray only safranins pink/red color.

I hope this helps!

-Ken