Can gram positive organisms also stain gram negative if correctly stained?

1. Can a Gram stain be positive and negative?
2. Why would a Gram-positive stain appear Gram-negative?
3. Which may result in Gram positive bacteria appearing to be Gram-negative?
4. What color would a Gram-positive and Gram-negative organism be stained?
5. Why do Gram positive and negative stain differently?
6. What do negative staining and positive staining have in common?
7. What happens when over Decolourised?
8. Is the positive control properly stained?
9. What factors can affect the results of a Gram stain and why?
10. What are the limitations of Gram staining method?
11. What can cause a false positive Gram stain?
12. Why is it important to know if bacteria is Gram positive or negative?
13. Why do Gram positive bacteria stain purple and Gram negative bacteria stain red?

Can a Gram stain be positive and negative?

A Gram stain is colored purple. When the stain combines with bacteria in a sample, the bacteria will either stay purple or turn pink or red. If the bacteria stays purple, they are Gram-positive. If the bacteria turns pink or red, they are Gram-negative.

Why would a Gram-positive stain appear Gram-negative?

Gram stain results are not always a conclusive test to indicate the structure of the cell wall of bacteria. Certain gram-positive bacteria lose some of their cell wall properties with age or exposure to harsh or bacterial static/ bactericidal agents causing them to appear gram-negative or gram-variable.

Which may result in Gram positive bacteria appearing to be Gram-negative?

When over-decolourized by either prolonged exposure to decolourizer or using acetone alone. When cell wall gets damaged by exposure to lysozyme or cell wall acting antibiotics such as Penicillin.

What color would a Gram-positive and Gram-negative organism be stained?

The staining procedure differentiates organisms of the domain Bacteria according to cell wall structure. Gram-positive cells have a thick peptidoglycan layer and stain blue to purple. Gram-negative cells have a thin peptidoglycan layer and stain red to pink.

Why do Gram positive and negative stain differently?

Gram-positive and Gram-negative bacteria stain differently because of fundamental differences in the structure of their cell walls. The bacterial cell wall serves to give the organism its size and shape as well as to prevent osmotic lysis. The material in the bacterial cell wall which confers rigidity is peptidoglycan.

What do negative staining and positive staining have in common?

Negative staining produces an outline or silhouette of the organisms against a colorful background (Figure 2). Because cells typically have negatively charged cell walls, the positive chromophores in basic dyes tend to stick to the cell walls, making them positive stains.

What happens when over Decolourised?

Although this smear is the proper thickness, it is not appropriate for examination because the host cells are stained blue instead of red, indicating that the smear was under-decolorized. In addition, small flecks of precipitated stain are present. ... If the smear is over-decolorized, the slide should be stained again.

Is the positive control properly stained?

If the Gram stain is performed properly, the positive control should appear purple (Gram-positive). As a Negative Control we use a known Gram-negative bacteria. In this simulation, Escherichia coli is used. If the Gram stain is performed properly, the negative control should appear pink (Gram-negative).

What factors can affect the results of a Gram stain and why?

The many variables that can affect this stain are age of the culture, amount of decolorizer used, the time of decolorization, the type of organism (acid-fast bacteria and spores do not stain well), thickness of the smear, and the general care of the stainer.

What are the limitations of Gram staining method?

Keep in mind the diagnostic limitations of sputum Gram's stain and culture, including the inability to visualize atypical organisms, contamination by oral flora, and the difficulty encountered by some patients to provide adequate specimens.

What can cause a false positive Gram stain?

Inappropriate specimen sampling, specimen processing, smear preparation, and prior antibiotic therapy are all factors that can have an adverse impact on Gram stain result. The inherent nature of some organisms may also produce misleading results; for example, Acinetobacter spp.

Why is it important to know if bacteria is Gram positive or negative?

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.

Why do Gram positive bacteria stain purple and Gram negative bacteria stain red?

Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50–90% of cell envelope), and as a result are stained purple by crystal violet, whereas gram-negative bacteria have a thinner layer (10% of cell envelope), so do not retain the purple stain and are counter-stained pink by safranin.