what is Gram Stain Technique with animation

Aim:

  To differentiate between the two major categories of bacteria: Gram positive and Gram negative.To understand how the Gram stain reaction affects Gram positive and Gram negative bacteria based on the biochemical and structural differences of  their cell walls. 

principle :Staining is an auxiliary technique  used in microscopic techniques used to enhance the clarity of the microscopic image.Stains and dyes are widely used in the scientific field to highlight the structure of the biological  specimens, cells, tissues etc.The most widely used  staining procedure  in microbiology  is the Gram stain, discovered by  the Danish scientist and physician Hans Christian Joachim Gram in 1884. Gram staining is a differential staining technique that differentiates bacteria into  two  groups: gram-positives and gram-negatives. The procedure is based on the ability of microorganisms to retain  color of the stains  used during the  gram stain reaction. Gram-negative bacteria are decolorized by the alcohol,  losing  the  color of  the primary stain, purple. Gram-positive  bacteria  are  not  decolorized by alcohol and will remain as purple. After  the decolorization step, a counterstain is used to impart a pink color to the decolorized gram-negative organisms.

Importance of a Gram Stain:

The Gram stain is a very important preliminary step in the initial characterization  and classification of bacteria.  It is also a key procedure in the identification of bacteria based on staining characteristics, enabling the bacteria to be examined using a light microscope.  The bacteria present in an unstained smear are invisible when viewed using a light microscope. Once stained, the morphology and arrangement of the bacteria may be observed as well. Furthermore, it is also an important step in the screening of  infectious agents in clinical specimens such as direct smears from a patient.

The Gram stain procedure enables bacteria to retain color of the stains, based on the differences in the chemical and physical properties of the cell wall.

     1. Gram positive bacteria: Stain dark purple due to retaining the primary dye called Crystal Violet in the cell wall.

                           Example: Staphylococcus aureus

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