Table of Contents
- 1 Does bacterial age affect Gram stain?
- 2 What is the best age for your culture when performing a Gram stain Why?
- 3 What are the limitations of Gram staining?
- 4 Why Will old more than 48 hours cultures of Gram positive bacteria stain as gram-negative?
- 5 Which is the optimum age for a valid Gram reaction?
- 6 Why is the Gram stain considered a differential stain?
Does bacterial age affect Gram stain?
Gram staining dependent on time periods for the staining, counter staining, alcohol wash and stain fixation. Yes, old culture can sometimes give false results. Cells with damages walls or dead cells can give gram negative result.
What will happen if you Gram stain cells of an old culture?
Cells from old cultures may stain Gram negative even if the bacteria are Gram positive. A Gram negative bacterium contains less peptidoglycan and more lipid than a Gram positive organism. These chemical characteristics cause more effective and rapid removal of dye complex when decolorizer is applied.
What factors can affect the Gram stain reaction?
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 is the best age for your culture when performing a Gram stain Why?
18-48 hours old
The most common reasons for false gram reactions? Some bacterial species tend towards gram variable, and will show both colors although most often gram +. Over decolorizing the smear, too long a time. Using old cultures (preferably, the cultures should be 18-48 hours old).
Why must cultures between 18 24 hours old be used for the gram stain?
It is recommended that young, actively growing cultures be used for gram staining. An intact cell wall is required for an accurate gram stain. Older cultures may have breaks in the cell wall and often give gram- variable results where a mixture of pink/red cells are seen among blue/purple cells.
Why will old 48 Hour cultures of Gram positive bacteria stain as gram-negative?
Old cultures tend to lose the peptidoglycan cell walls, which predisposes gram-positive cells to be gram-negative or gram variable. Gram stain is not useful for organisms without a cell wall like Mycoplasma species, and for smaller bacteria like Chlamydia and Rickettsia species.
What are the limitations of Gram staining?
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 would happen if you gram stained human cells?
If you performed a Gram stain on human cells, what would happen? NO cell walls, the cells would not hold the stain, ETOH (alcohol) would destroy the membranes (phospholipid bilayer).
How does the age of a culture affect the Gram stain reaction what is an optimum culture age for a valid gram reaction?
Old cultures can convert to gram-variable or gram-negative giving erroneous results. What is an optimum culture age for a valid gram reaction? Optimum age is 16-18 hours. If done too long, gram-positive can look gram-negative and if done too short, gram-negative and look gram-positive.
Why Will old more than 48 hours cultures of Gram positive bacteria stain as gram-negative?
Why is it important to use fresh cultures when performing Gram staining?
First, older bacterial cells may have damage to their cell walls that causes them to appear gram-negative even if the species is gram-positive. Thus, it is best to use fresh bacterial cultures for Gram staining. Second, errors such as leaving on decolorizer too long can affect the results.
Which step is most likely to cause poor results in the Gram stain?
the decolorization step
Excessive Decolorization It is clear that the decolorization step is the one most likely to cause problems in the Gram stain.
Which is the optimum age for a valid Gram reaction?
Old cultures can convert to gram-variable or gram-negative giving erroneous results. What is an optimum culture age for a valid gram reaction? Optimum age is 16-18 hours. Which step in the gram stain procedure is most prone to error?
What happens if you do a Gram stain too long?
If done incorrectly, how might that step affect the end result? If done too long, gram-positive can look gram-negative and if done too short, gram-negative and look gram-positive. Which reagent serves this purpose in the gram stain procedure?
Why does a Gram positive organism stain negatively?
There are several factors that could result in a gram-positive organism staining gram-negatively: 1. The method and techniques used. Overheating during heat fixation, over decolorization with alcohol, and even too much washing with water between steps may result in gram-positive bacteria losing the crystal violet-iodine complex. 2.
Why is the Gram stain considered a differential stain?
Terms in this set (20) Why is the gram stain considered a differential stain? It differentiates gram-positive and gram-negative cell walls based on staining. How do gram-positive and gram-negative bacteria differ in cellular structure, and how does this contribute to their differential staining properties?