What are four factors that affect the results of the Gram stain?
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 factors cause Gram variability?
Variations in Gram Reaction
- Cell wall damage of bacteria due to antibiotic therapy or excessive heat fixation of the smear.
- Over- decolorization of the smear.
- Use of an Iodine solution which is too old, i.e. yellow instead of brown in color (always store in a brown glass or other light opaque containers).
What are the 4 major steps in gram staining and what is the role of each reagent?
The performance of the Gram Stain on any sample requires 4 basic steps that include applying a primary stain (crystal violet) to a heat-fixed smear, followed by the addition of a mordant (Gram’s Iodine), rapid decolorization with alcohol, acetone, or a mixture of alcohol and acetone and lastly, counterstaining with …
What factors are important in achieving a good Gram stain?
Follow these best practices to perfect your Gram stain technique:
- Don’t make your smear too heavy.
- Always test your incoming stains and reagents.
- Use a fresh culture.
- Air dry the slide completely before fixing it.
- Fix the specimen on the slide by using heat or methanol.
- Don’t over-decolorize.
What is Gram variability how can it affect your results?
How can it affect your results? Gram variability is when the organism you are staining is a mix of red (gram negative) and purple (gram positive). The culture might be contaminated or old.
What is Gram variable?
Gram-variable organisms are those that cannot be grouped as either negative or positive. The appearance of organisms that stain gram-positive or -negative means that the smear contains organisms. These organisms may be pathogenic or nonpathogenic.
What are the factors or variables that a Gram-positive organism may become gram-negative and vice versa?
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 is Gram variability?
Definition of gram-variable : staining irregularly or inconsistently by Gram’s stain.
What are principles of Gram staining?
The basic principle of gram staining involves the ability of the bacterial cell wall to retain the crystal violet dye during solvent treatment. Gram-positive microorganisms have higher peptidoglycan content, whereas gram-negative organisms have higher lipid content.
What are the factors or variables that a Gram-positive organism may become Gram negative and vice versa?
What are the four stages of Gram staining?
The Gram staining process includes four basic steps, including:
- Applying a primary stain (crystal violet).
- Adding a mordant (Gram’s iodine).
- Rapid decolorization with ethanol, acetone or a mixture of both.
- Counterstaining with safranin.
How are bacteria Gram-variable?
These are a few bacteria species, which cannot be grouped as either gram-negative or gram-positive bacteria. This is mainly because, when these bacteria are stained in gram stain, they appear a mix of pink and purple cells. Therefore, they are classified into gram-variable bacteria.
What are examples of Gram-variable bacteria?
Gram-variable: bacteria that partially retain the purple color of the crystal violet in the Gram stain; most com- monly seen with Bacillus spp., Clostridium spp., Acineto- bacter spp., Streptococcus pneumoniae.
What is the major factor that determines if bacteria are Gram positive or gram negative?
The major difference between the two groups of bacteria is the thickness of the cell wall and the presence of an outer membrane in Gram negative bacteria only. The bacterial cell wall ranges from 20–80 nm thick for Gram positive and between 1.5–10 nm thick for Gram negative bacteria.
What is responsible for the differences in the Gram stain reactions?
The differences in cell wall composition of Gram-positive and Gram-negative bacteria account for the Gram staining differences. Gram-positive cell wall contains a thick layer of peptidoglycan with numerous teichoic acid cross-linking which resists the decolorization.
How are bacteria gram-variable?
Which cell component determines the results of the Gram stain?
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 is gram variability?
What is an example of a gram variable?
Bacilli: Escherichia coil, Pseudomonas species, Proteus species, and Klebsiella species. Examples of gram variable organisms include: Actinomyces species.
How are bacteria gram variable?
What are the factors that affect the rate of reaction?
Learning Objectives. We can identify five factors that affect the rates of chemical reactions: the chemical nature of the reacting substances, the state of subdivision (one large lump versus many small particles) of the reactants, the temperature of the reactants, the concentration of the reactants, and the presence of a catalyst.
What are the factors that affect the accuracy of Gram staining?
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. The most common reasons for false gram reactions?
Why do Gram variable reactions occur in mycobacteria?
Why do gram variable reactions occur? That depends on how you define “gram variable”. Mycobacteria have thick cell walls, enabling cells to retain the Gentian Violet-Iodine (GV-I) stain (which makes them appear gram positive), even though these walls have high lipid content (which would usually render them gram negative).
What are the most common reasons for false Gram reactions?
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 ).