Question of the Day

Gram-positive bacteria retain crystal violet iodine complex and appear blue or purple on a Gram-stained slide. Gram-negative and -positive bacteria do not stain differently with Dif Quik or other stains.

Follow this link to see BLUE gram-positive bacteria.

Gram-negative bacteria lose the iodine complex after it is washed out with alcohol and take up the secondary dye safranin, so stain red.

Follow this link to see RED gram-negative bacteria.