Gram staining

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One of the basic stains in microbiology, gram staining gave rise to the division of bacteria into Gram positive (G+) and Gram negative (G-). This division is based on the different structure of the bacterial wall.

Procedure[edit | edit source]

The sample or bacterial culture to be examined is applied to the slide and the staining solutions are gradually applied. Allow each solution to work for approximately 1 minute[1]. The procedure is easily remembered by the abbreviation VLAS (VLAK):

Gram coloring

Positivity and negativity[edit | edit source]

G+[edit | edit source]

Gram positive

Gram-positive bacteria have a wall composed of peptidoglycan and polysaccharides through which teichoic acid passes. During staining, the crystalline violet enters the cells and forms a blue complex color with Lugol's solution. The alcohol is unable to penetrate the cell wall and dissolve the complex. Safranin staining gives the bacteria a deep purple color.

G–[edit | edit source]

Gram negative

Gram-negative bacteria have a wall consisting of a thin layer of peptidoglycan and a layer of lipopolysaccharide. In the same process, the third step involves washing out of the complex with alcohol and decolorization. Safranin stains the bacteria red.

G labile and non-staining[edit | edit source]

Some bacteria, especially after long cultivation and multiple passaging, or if they survive the attack of antibiotics against the cell wall (L-forms), can change from G+ to G-.

Bacteria that contain a lot of fatty acids and waxes in their wall (Mycobacterium tuberculosis) can not be stained by Gram at all.

Links[edit | edit source]

Related articles[edit | edit source]

Source[edit | edit source]

  • RYŠKOVÁ, Olga. Návody k praktickým cvičením z lékařské mikrobiologie. 1. edition. Praha : Karolinum, 1997. ISBN 80-7184-307-5.

Reference[edit | edit source]

  1. JULÁK, Jaroslav. Praktická cvičení a semináře z lékařské mikrobiologie. 2. edition. Praha : Karolinum, 2009. 113 pp. ISBN 978-80-246-1141-9.

Source[edit | edit source]