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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
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 purpose of control test in gram stain?
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.
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.
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 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
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.
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.
Gram stain of skin lesion?
DefinitionA gram stain of a skin lesion is a laboratory test that uses special stains to detect and identify bacteria in a sample from a skin sore. The gram stain method is one of the most commonly used techniques for the rapid diagnosis of bacterial infections.Alternative NamesSkin lesion gram stainHow the test is performedYour health care provider will remove a sample of tissue from the skin sore. For information on how this is done, see the article on skin lesion biopsy.The sample is sent to a laboratory, where it is applied in a very thin layer to a glass slide. A series of different colored stains is applied to the sample. A laboratory team member examines the stained slide under a microscope, checking for bacteria. The color, size, and shape of the cells help identify the infecting organism.How to prepare for the testNo preparation is needed for the laboratory test.How the test will feelThe laboratory test is painless. For information on what it feels like to have the skin sample removed, see skin lesion biopsy.Why the test is performedYour doctor may order this test if you have signs of an infected skin sore. The test is done to determine which bacteria is causing the infection.Normal ValuesThe test is normal if no bacteria are identified.What abnormal results meanAn abnormal result means bacteria have been found in the skin lesion. Further tests are needed to confirm the results.What the risks areThere are no risks related to the laboratory test. For information on risks related to the removal of a skin sample, see skin lesion biopsy.Special considerationsA skin or mucosal culture may be done along with this test. Other studies are often done on a skin sample to determine if cancer is present.Viral skin lesions, like herpes simplex, are examined by other tests or a viral culture.
What is a cytology laboratory test?
its a urine test
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.
