Gram staining is based on:a) the ability of the bacterial cell wall to retain crystal violet dyeb) the lysis of bacterial cellsc) differences in bacterial shape and sized) growth of bacterial cells
Question
Gram staining is based on:a) the ability of the bacterial cell wall to retain crystal violet dyeb) the lysis of bacterial cellsc) differences in bacterial shape and sized) growth of bacterial cells
Solution
Gram staining is based on the ability of the bacterial cell wall to retain crystal violet dye. This method is used to differentiate bacterial species into two large groups: Gram-positive and Gram-negative. The names come from the Danish bacteriologist Hans Christian Gram, who developed the technique.
Here are the steps of the Gram stain process:
- A heat-fixed smear of bacterial cells is stained with crystal violet (the primary stain).
- The smear is then washed with a mordant – usually Gram's iodine solution – which forms a complex between the crystal violet and the cell wall.
- The smear is then washed with a decolorizer, such as alcohol or acetone, which dehydrates the peptidoglycan layer, shrinking and tightening it. The large crystal violet-iodine complexes are not able to penetrate this tightened peptidoglycan layer, and are thus trapped in the cell in Gram-positive bacteria. Conversely, the outer membrane of Gram-negative bacteria is degraded and the thinner peptidoglycan layer of Gram-negative cells is unable to retain the crystal violet-iodine complex and the color is lost.
- A counterstain, such as the weakly staining safranin, is added to the sample, staining it red. Since the safranin does not disrupt the crystal violet staining already present in Gram-positive cells, these cells remain purple, while the decolorized Gram-negative cells take up the red counterstain.
So, the correct answer to your question is a) the ability of the bacterial cell wall to retain crystal violet dye.
Similar Questions
Gram staining involves three steps: 1. crystal violet (purple) staining, 2. decolorization, 3. counterstaining (red). If you look under a microscope after the first step, you will see that:Group of answer choicesonly gram negative bacteria are purpleonly gram positive bacteria are purpleboth gram positive and negative bacteria are purpleneither gram positive and negative bacteria are purple
What structure does the gram stain characterize?
Why must fresh cells be used when performing a Gram stain?
You are performing a Gram stain on gram-positive bacteria and you stop after the addition of the first dye. What is the appearance of the bacteria at this point?Question 13Answera.purpleb.colorlessc.redd.brown
Assume you stain Bacillus by applying malachite green with heatand then counterstain with safranin. Through the microscope, thegreen structures area. cell walls.b. capsules.c. endospores.d. flagella.e. impossible to identify.2. Live cells at a depth of 1 mm and with reduced phototoxicity canbe viewed through aa. darkfield microscope.b. fluorescence microscope.c. two-photon microscope.d. confocal microscope.e. phase-contrast microscope.3. Capsule staining is a difficult technique to accomplish becausea. capsules are antigenic.b. capsules repel most biological dyes.c. capsular materials are water soluble.d. the specimen has to be mixed with fine colloidal suspension ofIndia ink or nigrosin.4. You observe that the cells of a Gram-stained urine sample appearpurple in brightfield microscopy, with cocci-shaped bacteriaarranged in chains. You conclude:a. the urine sample is too old.b. the smear is too thick.c. gram staining is unsuitable for this sample.d. the cells are gram-positive.e. none of the above.5. Which of the following is not a functionally analogous pair of stains?a. nigrosin and malachite greenb. crystal violet and carbolfuchsinc. safranin and methylene blued. ethanol-acetone and acid-alcohole. All of the above pairs are functionally analogous.6. Which of the following pairs is mismatched?a. capsule—negative stainb. cell arrangement—simple stainc. cell size—negative staind. Gram stain—bacterial identificatione. none of the above7. Assume you stain Clostridium by applying a basic stain,carbolfuchsin, with heat, decolorizing with acid-alcohol, andcounterstaining with an acidic stain, nigrosin. Through themicroscope, the endospores are 1 , and the cells are stained2 .a. 1—red; 2—blackb. 1—black; 2—colorlessc. 1—colorless; 2—blackd. 1—red; 2—colorlesse. 1—black; 2—red8. Assume that you are viewing a Gram-stained field of red cocci andblue rods through the microscope. You can safely conclude thatyou havea. made a mistake in staining.b. two different species.c. old bacterial cells.d. young bacterial cells.e. none of the above9. In 1996, scientists described a new tapeworm parasite that hadkilled at least one person. The initial examination of the patient’sabdominal mass was most likely made usinga. brightfield microscopy.b. darkfield microscopy.c. electron microscopy.d. phase-contrast microscopy.e. fluorescence microscopy
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