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Gram staining is a simple staining test that simply identifies the two main groups of bacteria. Gram positive, and gram negative.
Down a microscope, gram pos look like a dark blue/purple colour, and gram neg look red. It is to do with what the wall of the bacteria comprises of, and without going into too much detail, certain drugs work on gram pos bacteria, and others wont. Likewise for gram neg.
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∙ 12y ago
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∙ 14y agoThe reason why we need a control when doing a gram stain is to compare. sometimes the gram negative looks like its purple and not pink. unless you have a control stain to compare it with, its really hard to differentiate
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∙ 11y agoThe main purpose of the safranin counterstain in Gram Staining is to stain gram negative bacteria left over from not picking up the crystal violet dye that stains gram positive microorganisms. It allows the view and identification of gram negative bacteria.
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∙ 11y agoFirst to stain the organism. Gram stain differentiates organisms in to gram positive and gram negative. This will help the microbiologist to choose which media to use to grow them, have a clue what might be the organism is, etc.
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∙ 14y agoTo determine if bacteria is gram positive or gram negative
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∙ 14y agoits purpose is to classify bacteria
Wiki User
∙ 10y agofor comparison purposes
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What is the purpose of a TSI test?
To differentiate among the different groups or genera of the Enterobacteriaceae, which are all gram-negative bacilli.
What is the purpose of a control plate?
A control plate in microbiology is used given a bacteria with a known reaction to the test. This is done to compare to some unknown bacteria undergoing the test.
Why would gram negative bacteria appear purple after gram stain?
The simple staining procedure makes to visualize bacteria clearly, but it does not distinguish between organisms of similar morphology. The Gram staining method is named after the Danish bacteriologist (1882) Hans Christian Gram, is one of the most important staining techniques in microbiology. It is almost always the first test performed for the identification of bacteria. The primary stain of the Gram's method is crystal violet. Crystal violet is sometimes substituted with methylene blue, which is equally effective. The microorganisms that retain the crystal violet-iodine complex appear purple brown under microscopic examination. These microorganisms that are stained by the Gram's method are commonly classified as Gram-positive or Gram non-negative. Others that are not stained by crystal violet are referred to as Gram negative, and appear red. In this method the fixed bacterial smear is subjected to the following staining reagents in the order of sequence listed below Primary stain Crystal violet is used first and stains all cell purple = Mordant = Grams iodine serves as a mordant, a substance that increases the cell affinity for a stain. It does this by binding to the primary stain thus forming an insoluble complex. The resultant crystal violet iodine complex serves to identify the color of the stain. At this point all cells will appear purple black. = Decolorizing agent = Gram staining is based on the ability of bacteria cell wall to retaining the crystal violet dye during solvent treatment. The cell walls for Gram-positive microorganisms have a higher peptidoglycan and lower lipid content than gram-negative bacteria In Gram-negative cells, subsequent treatment with a decolorizer, (95% ethyl alcohol) dissolves the lipid layer from the gram-negative cells. The removal of the lipid layer enhances the leaching of the primary stain from the cells into the surrounding solvent. In contrast, the solvent dehydrates the thicker Gram-positive cell walls, closing the pores as the cell wall shrinks during dehydration. As a result, the diffusion of the violet-iodine complex is blocked, and the bacteria remain stained. Counter stain A counterstain of basic fuchsin or saffranin is applied to the smear to give decolorized gram-negative bacteria a pink color. Since only gram-negative cells undergo decolorization they may now absorb the counter stain. Gram-positive cell retain the purple color of the primary stain. Basic fuchsin stains many Gram-negative bacteria more intensely than does safranin, making them easier to see. Some bacteria which are poorly stained by safranin, such as Haemophilus spp., Legionella spp., and some anaerobic bacteria, are readily stained by basic fuchsin, but not safranin. The polychromatic nature of the gram stain enables determination of the size and shape of both Gram-negative and Gram-positive bacteria. If desired, the slides can be permanently mounted and preserved for record keeping.
Why are some bacteria gram-positive and some gram-negative?
During a gram stain some bacteria retains the stain because they are gram positive with thicker walls . If the bacteria does not stain either it is an endospore bacteria or gram negative with thinner walls, so colorless or red color.
Why must fresh bacterial cultures be used in a Gram stain?
Why must young cultures be used when doing a Gram stain Young cultures must be used so the crystal violet can stick to the cell walls of Gram positive bacteria. The cell walls break down in old cultures and the staining process is not accurate
Biochemical tests to confirm micrococcus luteus?
I had a bacterial unknown of M. luteus in my microbiology lab. M. luteus is a Gram positive cocci (as seen by a gram stain). A good definitive test for Gram + cocci is the catalase test. M. luteus is catalase positive. Then a nitrate test can be performed to determine that M. luteus is nitrate negative. Those alone should be enough to confirm M. luteus.
What is the test that separates enterococcus faecalis and lactococcus lactis?
To diagnose Enterococcus faecalis: (Facultative anaerobic) First, do the Gram stain: Gram positive cocci in chains catalase test: negative PYR disc: positive
Can Gram-positive organism appear as Gram-negative?
Staphylococcus are Gram positive because, in Gram's test, the decolorizing agent (ETOH) cannot penetrate the thick cell walls, and the stain remains behind: hence Gram positive. I am not aware of a gram negative staph species and, considering the degree of mutation that would be needed to form such a strain, I do not believe that it's possible. I should add that a not-so-brief scan of the net showed me no Gram negative staph mentioned anywhere. So -- for now -- no. That said, let's see what the future holds.
What is the purpose of sodium azide in the Bile Esculin test?
The purpose of the bile esculen azide agar is to inhibit the growth of gram-positive organisms.
What is the purpose of a TSI test?
To differentiate among the different groups or genera of the Enterobacteriaceae, which are all gram-negative bacilli.
What is the best biochemical test to identify gram negative and H2S bacilli?
Gram Stain to determine gram negative and shape or streak on a Agar plate selective for gram negative such as Desoxycholate Agar (DES). A SIM (Sulfur, Indole, Motility) Test or a Kiliger's Iron Agar (KIA) Test can confirm the production of H2S. *I would choose Streaking on DES to isolate the gram Negative bacteria, and then stab inoculate a SIM tube. Black precipitate confirms H2S production positive.
Is it necessary to follow up Gram staining with KOH test?
Gram staining allows you to visualize bacteria and cells. I would only follow a Gram stain with a KOH test if I didn't find anything pathogenic or interesting to look at on the Gram stained slide. The KOH test breaks down large structures (usually hairs) that may be holding or blocking the visualization of pathogenic organisms. It is very useful on skin scrapings to look for ringworm, but otherwise it's not that useful clinically.
What is the purpose of a control plate?
A control plate in microbiology is used given a bacteria with a known reaction to the test. This is done to compare to some unknown bacteria undergoing the test.
Why would gram negative bacteria appear purple after gram stain?
The simple staining procedure makes to visualize bacteria clearly, but it does not distinguish between organisms of similar morphology. The Gram staining method is named after the Danish bacteriologist (1882) Hans Christian Gram, is one of the most important staining techniques in microbiology. It is almost always the first test performed for the identification of bacteria. The primary stain of the Gram's method is crystal violet. Crystal violet is sometimes substituted with methylene blue, which is equally effective. The microorganisms that retain the crystal violet-iodine complex appear purple brown under microscopic examination. These microorganisms that are stained by the Gram's method are commonly classified as Gram-positive or Gram non-negative. Others that are not stained by crystal violet are referred to as Gram negative, and appear red. In this method the fixed bacterial smear is subjected to the following staining reagents in the order of sequence listed below Primary stain Crystal violet is used first and stains all cell purple = Mordant = Grams iodine serves as a mordant, a substance that increases the cell affinity for a stain. It does this by binding to the primary stain thus forming an insoluble complex. The resultant crystal violet iodine complex serves to identify the color of the stain. At this point all cells will appear purple black. = Decolorizing agent = Gram staining is based on the ability of bacteria cell wall to retaining the crystal violet dye during solvent treatment. The cell walls for Gram-positive microorganisms have a higher peptidoglycan and lower lipid content than gram-negative bacteria In Gram-negative cells, subsequent treatment with a decolorizer, (95% ethyl alcohol) dissolves the lipid layer from the gram-negative cells. The removal of the lipid layer enhances the leaching of the primary stain from the cells into the surrounding solvent. In contrast, the solvent dehydrates the thicker Gram-positive cell walls, closing the pores as the cell wall shrinks during dehydration. As a result, the diffusion of the violet-iodine complex is blocked, and the bacteria remain stained. Counter stain A counterstain of basic fuchsin or saffranin is applied to the smear to give decolorized gram-negative bacteria a pink color. Since only gram-negative cells undergo decolorization they may now absorb the counter stain. Gram-positive cell retain the purple color of the primary stain. Basic fuchsin stains many Gram-negative bacteria more intensely than does safranin, making them easier to see. Some bacteria which are poorly stained by safranin, such as Haemophilus spp., Legionella spp., and some anaerobic bacteria, are readily stained by basic fuchsin, but not safranin. The polychromatic nature of the gram stain enables determination of the size and shape of both Gram-negative and Gram-positive bacteria. If desired, the slides can be permanently mounted and preserved for record keeping.
Why are some bacteria gram-positive and some gram-negative?
During a gram stain some bacteria retains the stain because they are gram positive with thicker walls . If the bacteria does not stain either it is an endospore bacteria or gram negative with thinner walls, so colorless or red color.
Why must fresh bacterial cultures be used in a Gram stain?
Why must young cultures be used when doing a Gram stain Young cultures must be used so the crystal violet can stick to the cell walls of Gram positive bacteria. The cell walls break down in old cultures and the staining process is not accurate
Would it be useful to perform a gram stain on a mixed culture?
The purity of a culture of bacteria is important so it can test on that one type of bacteria. Gram staining can be good so you make sure everything in the streak plate is one color showing that it is gram positive and gram negative.
