Explain how a bacterial cell may stain Gramnegative but not

Explain how a bacterial cell may stain Gram-negative, but not have a typical Gram-negative cell wall structure.

Solution

Gram negative bacterial cell : The outer membrane of Gram-negative bacteria contains lipopolysaccharides,proteins and phospholipids.The cell wall is composed of a single layer of peptidoglycan.Mycobacteria have a cell envelope whcih is not typical of Gram-positive of Gram-negative.Mycobacterium contain large amounts of lipids substance called mycolic acids.Mycolic acids resist staining such as Gram staining method. Ziehl-Neelsen technique (ZN) method of Acid Fast staining technique is used to stain mycobacterium sp such as M. tuberculosis.

Reagents required = primary stain 0.3% Carbol fuchsin , decolorization agent : 25% sulphuric acid , Malachite green 0.3% or methylene blue

Principle = Application of carbol fuchsin --> application of heat --> application of acid alcohol --> application of methylene blue.