If you have a mixed (Gram positive and Gram negative) sample, and you complete a Gram stain, and all the cells are purple at the end of the stain, what have you done wrong? forgotten safranin forgotten crystal violet forgotten decolorizer forgotten iodine everything worked perfectly

On the basis of lipid content in cell wall of bacteria these are classified into two types : Gram positive and Gram negative bacteria. 

These two are differentiated with the help of gram staining procedure.             The basis of gram staining is the lipid content of bacteria. Gram negative bacteria have high lipid content due to which the lipids dissolve in organic solvent taking out the stain along with itself.