<unk>  bacteria are those that retain a crystal violet dye during the Gram stain process.<unk>  bacteria appear blue or violet under a microscope, while Gram-negative bacteria appear red or pink. The Gram classification system is empirical, and largely based on differences in cell wall structure. The purpose of Gram staining is to visually differentiate groups of bacteria, primarily for identification.
Gram-positive
Gram-negative
Acid-fast
Gram-negative bacteria
Liquid
Pedunculated
Hydrophobe
Oncogenic