What factors may cause a false Gram reaction to be observed?

The Gram staining reaction, therefore, may be misleading, both for classification and for proper identification. A ‘false negative’ or a ‘false positive’ staining reaction may be due to (1) the properties of the organism itself, (2) the age of the culture or (3) the method applied.

Why do Gram positive bacteria sometimes appear purple and sometimes pink?

Under a microscope, gram-positive bacteria appear purple-blue because their thick peptidoglycan membrane can hold the dye. The bacteria is called gram-positive due to the positive result. Gram-negative bacteria stain pink-red. Their peptidoglycan layer is thinner, so it doesn’t retain the blue color.

What causes the difference in Gram staining in bacteria?

The Gram stain procedure distinguishes between Gram positive and Gram negative groups by coloring these cells red or violet. Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.

What are the main reasons for getting false positive or false negative in Gram stain?

Positive Gram stains with negative culture results could be due to fastidious or nonviable organisms and failure to order appropriate testing, such as anaerobe cultures. False-negative Gram stains could occur due to inadequate specimen or smear preparation or failure to examine an adequate number of fields.

What are the common sources of Gram staining errors?

The rank of errors is:

• Over decolourisation.
• Mixed cultures.
• Misread stains.
• Aged subcultures.
• Disorganisation.
• Inadequate fixation and Insufficient culture.

Why do we use positive and negative controls in the Gram stain?

The positive and negative controls are bacterial smears we use to test if the Gram stain was performed properly. If the positive and negative controls are not as expected, you can not trust that the stain was performed properly. As a Positive Control we use a known Gram-positive bacteria.

What is the current theory about the mechanism of the Gram stain reaction?

With the current theory behind Gram staining, it is thought that in Gram-positive bacteria, the crystal violet and iodine combine to form a larger molecule that precipitates out within the cell.

What is the purpose of Gram staining?

A Gram stain is most often used to find out if you have a bacterial infection. If you do, the test will show if your infection is Gram-positive or Gram-negative. A Gram stain may also be used to diagnose fungal infections.

Why might it be important to perform a Gram stain?

The main benefit of a gram stain is that it helps your doctor learn if you have a bacterial infection, and it determines what type of bacteria are causing it. This can help your doctor determine an effective treatment plan.

What might cause a gram positive cell to appear gram negative?

If the decolorizing agent is applied on the cell for too long time, the Gram-positive organisms to appear Gram-negative. Under-decolorization occurs when the alcohol is not left on long enough to wash out the CV-I complex from the Gram-negative cells, resulting in Gram-negative bacteria to appear Gram-positive.

What are the reasons false negative occur with Gram staining of tissue bacteria?

Why might Gram staining fail sometimes?

Gram-positive bacteria may lose their ability to retain crystal violet and stain Gram negatively for the following reasons: Cell wall damage of bacteria due to antibiotic therapy or excessive heat fixation of the smear. Over- decolorization of the smear.

What are the variations in the gram reaction?

Variations in Gram Reaction. Gram-positive bacteria may lose their ability to retain crystal violet and stain Gram negatively for the following reasons: Cell wall damage of bacteria due to antibiotic therapy or excessive heat fixation of the smear.

What is a Gram variable cell?

Gram variable cells will have cells that stain pink and cells that stain purple in the same sample. Gram variable bacteria have a cell wall structure that is like that of Gram positive bacteria, but for various reasons sometimes look Gram negative under the microscope. Also, what are gram rods?

What causes Gram staining to change?

Variations in Gram Reaction Gram-positive bacteria may lose their ability to retain crystal violet and stain Gram negatively for the following reasons: Cell wall damage of bacteria due to antibiotic therapy or excessive heat fixation of the smear. Over- decolorization of the smear

What is the difference between Gram positive and Gram negative cells?

When they are Gram stained, the Gram positive cells stain purple, while the Gram negative cells stain pink. Gram variable cells will have cells that stain pink and cells that stain purple in the same sample. Some genera, like Clostridium (which includes the species that cause botulism, tetanus