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After Gram Staining, We use counter staining to find out that is there any gram(-) bacteria present on the prepared slide.

My question is-

What component in the cell wall of gram(-) bacteria is responsible for the retention of Safranin dye? Like the Techoic Acid is responsible for the retention of CVI complex in gram (+) bacteria.

As I have just studied the staining process,any additional useful information is appreciated.

Thanks!

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I find it hard to find actual literature on this, so this is just my reasoning. Safranin is a basic dye (ie positively charged). I suspect electrostatic interactions with negative charges on phospholipids in the inner membrane are responsible for its retention.

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  • $\begingroup$ @canadianer- thanks! Your explanation helped a lot. If you can find any literature related to this, can you please post it? :) $\endgroup$ Commented Mar 3, 2017 at 13:51
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Safranin is retained, very much like Crystal violet, by the peptidoglycans in the cell wall. However, the main difference is the thickness of the peptidoglycan layers in Gram positive and Gram negative bacteria.

Gram positive bacteria, due to their thicker peptidoglycan layer, have a higher affinity to and retention rate of crystal violet. On the other hand, Gram negative bacteria, due to a thinner peptidoglycan layer cannot retain crystal violet as well and are more likely to retain safranin.

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