60. Given below are two statements: one is labelled as Assertion A and the other is labelled as
Reason R
Assertion A: Mycoplasma is a bacteria without cell wall, and it stains negative in Gram staining.
Reason R: Only bacteria that have a cell wall would stain positive in Gram staining.
In the light of the above statements, choose the correct answer from the options given below:
A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Introduction:

Gram staining is a common laboratory technique used to classify bacteria into two broad categories: Gram-positive and Gram-negative. The process is based on the structure of the bacterial cell wall. However, some bacteria, like Mycoplasma, do not possess a traditional cell wall and therefore do not follow the same staining patterns. Let’s explore how Mycoplasma behaves in Gram staining and the reasons behind this phenomenon.

What is Mycoplasma?

Mycoplasma is a unique genus of bacteria characterized by the absence of a cell wall. This distinctive feature sets Mycoplasma apart from most other bacteria, which typically possess a cell wall made of peptidoglycan. Due to the lack of a cell wall, Mycoplasma exhibits a flexible and pleomorphic (variable in shape) nature, which is different from typical bacteria that have rigid cell wall structures.

Gram Staining and Its Principle:

In Gram staining, bacterial cells are treated with a series of reagents, including a crystal violet stain followed by an iodine solution, and then a decolorization step using alcohol. After this, the cells are stained with safranin.

• Gram-positive bacteria retain the crystal violet stain and appear purple because of their thick peptidoglycan cell wall.

• Gram-negative bacteria, which have a thinner peptidoglycan layer, lose the crystal violet stain and take up the safranin, appearing pink.

The cell wall plays a critical role in retaining the crystal violet stain, but bacteria that lack a cell wall, like Mycoplasma, do not stain with the crystal violet and thus appear Gram-negative.

Mycoplasma and Gram Staining:

Because Mycoplasma lacks a cell wall, it does not retain the crystal violet stain during the Gram staining process. As a result, Mycoplasma appears Gram-negative. However, this result does not reflect the true Gram-negative nature of Mycoplasma because the absence of a cell wall is the key factor causing this result, not the typical characteristics of Gram-negative bacteria.

Analysis of the Statements:

• Assertion A: “Mycoplasma is a bacteria without cell wall, and it stains negative in Gram staining.”
  This statement is true. Mycoplasma indeed lacks a cell wall, and this causes it to stain negative in Gram staining.

• Reason R: “Only bacteria that have a cell wall would stain positive in Gram staining.”
  This statement is false. While most Gram-positive bacteria do have a thick cell wall, Gram-negative bacteria also have a cell wall, though thinner. The reason some bacteria stain positive or negative is not solely dependent on whether they have a cell wall but on the structure and thickness of the cell wall and how it interacts with the Gram stain.

Conclusion:

The correct answer is C. A is true but R is false, because although Mycoplasma lacks a cell wall and stains negative, the explanation in Reason R about cell walls being required for Gram-positive staining is inaccurate. Mycoplasma’s Gram-negative result is due to its lack of a cell wall, not a general rule about bacterial cell walls.

Answer:

C. A is true but R is false