During Gram staining, which type of bacteria retains the crystal violet stain?

During Gram staining, which type of bacteria retains the crystal violet stain?

• A. Gram-negative bacteria
• B. Gram-positive bacteria
• C. Mycoplasmas
• D. Spirilla

Answer: (B)

The retention of the crystal violet stain during the Gram staining process is a characteristic feature of Gram-positive bacteria. These bacteria have a thick peptidoglycan layer in their cell wall, which traps the crystal violet dye. When the Gram stain procedure is conducted, after applying the crystal violet followed by iodine, a complex forms within the thick peptidoglycan layer. This results in the dye being retained even after a decolorization step, typically involving alcohol or acetone. In contrast, Gram-negative bacteria, which have a much thinner peptidoglycan layer surrounded by an outer membrane, do not retain the crystal violet stain. Instead, they take up the counterstain, often safranin, resulting in a pink appearance. Mycoplasmas, lacking a cell wall, do not fit into the Gram classification system and will not retain the crystal violet. Spirilla, being a form of bacteria that can be either Gram-positive or Gram-negative, do not consistently retain the stain, as their Gram classification depends on the specific species and their cell wall structure. Thus, Gram-positive bacteria are specifically noted for their ability to retain the crystal violet stain, making them appear purple under the microscope after the Gram staining procedure.

The retention of the crystal violet stain during the Gram staining process is a characteristic feature of Gram-positive bacteria. These bacteria have a thick peptidoglycan layer in their cell wall, which traps the crystal violet dye. When the Gram stain procedure is conducted, after applying the crystal violet followed by iodine, a complex forms within the thick peptidoglycan layer. This results in the dye being retained even after a decolorization step, typically involving alcohol or acetone.

In contrast, Gram-negative bacteria, which have a much thinner peptidoglycan layer surrounded by an outer membrane, do not retain the crystal violet stain. Instead, they take up the counterstain, often safranin, resulting in a pink appearance. Mycoplasmas, lacking a cell wall, do not fit into the Gram classification system and will not retain the crystal violet. Spirilla, being a form of bacteria that can be either Gram-positive or Gram-negative, do not consistently retain the stain, as their Gram classification depends on the specific species and their cell wall structure.

Thus, Gram-positive bacteria are specifically noted for their ability to retain the crystal violet stain, making them appear purple under the microscope after the Gram staining procedure.