# Gram Stain vs Acid-Fast Stain – Key Differences

> Gram stain refers to a staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent...

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Author: Sourav Pan
Last updated: August 22, 2026

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## Comparison Between Gram Stain and Acid Fast

S.NoCharacteristicsGram StainAcid Fast1DefinitionGram stain refers to a staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye.The acid-fast stain refers to a differential stain used to identify acid-fast organisms such as members of the genus Mycobacterium.2PurposeGram stain is used to distinguish between gram-positive bacteria and gram-negative bacteria.A cid-fast stain is used to distinguish between acid-fast bacteria and non-acid fast bacteria.3Type of characterizationGram stain characterizes bacteria with different types of cell wallsAcid-fast stain characterizes bacteria with mycolic acid in the cell wall.4Primary StainCrystal violet is used as a primary stain in Gram staining.Carbol fuchsin is used as a primary stain in Acid Fast staining.5MordantIodine is used as mordant in Gram staining.Phenol acts as a mordant in Acid Fast staining.6CounterStainSafranin is used as a counterstain in Gram staining.Methylene blue is used as a counterstain in Acid Fast staining.7AppearingIn Gram stain, Gram-positive bacteria appear in blue color while Gram-negative bacteria appear in red color.In acid-fast stain, acid-fast bacteria appear in red color while non-acid-fast bacteria appear in blue color.8MicroorganismsExample of Gram-Positive Bacteria: Lactobacillus, Nocardia, Bacillus, Clostridium, Staphylococcus, Propionibacterium, Actinomyces, Streptomyces, Enterococcus, Listria,Gardnerella, Cornyebacterium, Mycoplasma, Streptococcus.
Example of Gram-Negative Bacteria: Helicobcater, Escherichia, Shigella, Hemophilus, Neisseria, Pseudomonas, Klebsiella, Enterobacter, Vibrio, Chlamydia, Salmonella.Nocardia spp (Partial Acid Fast), Rhodococcus spp (Partial Acid Fast), Legionella micdadei (Partial Acid Fast in tissue), Cyst of Cryptosporidium (Acid Fast), Cyst of Isospora (Acid Fast)