Quiz On Gram Stain

The correct answer is 4 because the Gram stain technique requires the use of four different reagents. These reagents include crystal violet, iodine, ethanol or acetone, and safranin. Each reagent plays a specific role in the staining process, which helps to differentiate between Gram-positive and Gram-negative bacteria. Crystal violet stains all bacteria, iodine acts as a mordant to fix the stain, ethanol or acetone is used as a decolorizer to remove the stain from Gram-negative bacteria, and safranin is a counterstain that stains the Gram-negative bacteria pink. Therefore, four reagents are necessary for a complete Gram stain procedure.

Staphylococcus epidermidis is the correct answer because it is a Gram-positive bacterium that has a spherical shape (coccus) and grows in clusters or bunches. Bacillus cereus is a Gram-positive bacterium, but it has a rod-shaped (bacillus) morphology. Micrococcus luteus is also a Gram-positive bacterium, but it typically grows in tetrads or irregular clusters, not bunches. Escherichia coli is a Gram-negative bacterium and does not have a spherical shape or grow in bunches.

Iodine is used as a mordant because it has the ability to fix dyes to fabrics and enhance their colorfastness. Mordants are substances that are used in dyeing and printing processes to improve the adherence of dyes to the fibers of the material being dyed. They create a chemical bond between the dye and the fabric, making the color more permanent and resistant to fading. Iodine, with its strong affinity for certain dyes, acts as an effective mordant in dyeing processes.

The Gram staining method was developed by Christian Gram. He was a Danish bacteriologist who invented this technique in 1884. The method is used to differentiate bacteria into two major groups, Gram-positive and Gram-negative, based on the differences in their cell wall structure. This staining method has been widely used in microbiology to identify and classify bacteria, as well as to guide treatment decisions in clinical settings.

Gram-negative bacteria may appear red after Gram staining because they have a thinner peptidoglycan layer in their cell wall. During the Gram staining process, the bacteria are first stained with crystal violet dye, then treated with iodine, which forms a complex with the dye. When the bacteria are washed with alcohol or acetone, the outer membrane of Gram-negative bacteria is disrupted, leading to the loss of the crystal violet-iodine complex. As a result, the bacteria do not retain the initial purple color and instead take up the counterstain safranin, which appears red under the microscope.

The cell wall of Gram-negative bacteria contains lipopolysaccharides (LPS). Gram-negative bacteria have a unique cell wall structure that includes an outer membrane containing LPS, which is a complex molecule made up of lipids and carbohydrates. This outer membrane is distinct from the peptidoglycan layer found in both Gram-positive and Gram-negative bacteria. Gram-positive bacteria, on the other hand, lack the outer membrane and do not contain LPS in their cell walls.

The Gram staining method was developed in 1883. This method is used to differentiate bacteria into two major groups, Gram-positive and Gram-negative, based on the differences in their cell wall composition. The method was named after the Danish bacteriologist Hans Christian Gram, who developed it. Gram staining has since become one of the most important techniques in microbiology and is widely used in the identification and classification of bacteria.

Escherichia coli is a Gram-negative bacterium that is cylindrical in shape, commonly known as a bacillus. It grows in pairs, which means that two cells are attached to each other. Micrococcus luteus is a Gram-positive bacterium and does not match the given characteristics. Staphylococcus epidermidis is also Gram-positive and typically grows in clusters, not pairs. Bacillus cereus is a Gram-positive bacterium and has a rod-like shape, but it does not grow in pairs. Therefore, the correct answer is Escherichia coli.

Gram stain differentiates bacteria on the basis of lipid and peptidoglycan concentration in the cell wall. This staining technique involves the use of crystal violet dye, iodine, alcohol, and safranin. Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which retains the crystal violet dye and appears purple under a microscope. Gram-negative bacteria have a thinner layer of peptidoglycan and an outer membrane containing lipids. The alcohol decolorizes the Gram-negative bacteria, making them appear pink when stained with safranin. Therefore, the presence of lipids and peptidoglycan in the cell wall is what allows the differentiation between Gram-positive and Gram-negative bacteria.

If acid-alcohol was used as a decolorizer instead of 95% ethyl alcohol in the Gram staining procedure, the color of Gram-positive bacteria would be red. This is because acid-alcohol is a stronger decolorizer than ethyl alcohol, and it would remove the crystal violet stain from the Gram-positive bacteria, causing them to appear red after the counterstain with safranin.