Biomedical Engineer Question:

In gram staining protocol, gram positive bacteria are stained dark blue or violet. Crystal violet stain can be retained by the gram positive bacteria because of the high amount of the peptidoglycan in the cell wall. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria.
In gram staining protocol, gram negative bacteria do not retain crystal violet dye. Gram negative bacteria have pathogenic capability. Gram negative bacteria have cytoplasmic membrane which is not present in gram positive bacteria.