Re: Gram stain procedure; using different colored dyes

Gram staining depends on the presence of cell wall peptidoglycan in the bacterial cell. It is seen that Gram-positive bacterial cell wall contains higher amount of peptidoglycan as compared to Gram-negative cells. Gram-positive reactions will stain dark blue-black and gram- negative reactions will stain deep pink or reddish.

Crystal violet stain is a primary stain, which stains the cell wall of Gram positive blue. Gram's iodine helps in penetration of crystal violet and adheres to gram-positive organisms. There are reports of using carbol fuschin in place of safranin as the counter-stain that stains the smear that has been decolorized.

Preston and Morrell's (1962) had modified the Gram staining method using ammonium oxalate and methylated spirit with crystal violet for color enhancement and proper differentiation.

You can use other basic stains apart from Crystal violet and safranin for staining the cells as suggested in most of the modified Gram staining methods. Also other color combinations can be used for staining the bacterial cells but the important point here is that of contrast and how readily we can differentiate the Gram-positive cells from that of Gram negative ones.

Regards,

Devendra

References:
http://www.maexamhelp.com/id121.htm
http://www.pubmedcentral.gov/picrender.fcgi?artid=474501&blobtype=pdf