Exercise 4 Gram Stain

What is the purpose of a Gram stain?

To differentiate Gram-positive bacteria from Gram-negative bacteria based on differences in their cell walls.

What is a differential stain?

A stain that uses different dyes to distinguish cells based on specific characteristics.

What is peptidoglycan?

A major structural component of the bacterial cell wall.

Which type of bacteria has a thick peptidoglycan layer?

Gram-positive bacteria.

Which type of bacteria has a thin peptidoglycan layer and an outer membrane?

Gram-negative bacteria.

What is the primary stain used in the Gram stain?

Crystal violet.

What is the mordant used in the Gram stain?

Gram's iodine.

What is the decolorizer used in the Gram stain?

Ethyl alcohol.

What is the counterstain used in the Gram stain?

Safranin.

What are the three types of information revealed by bacterial staining?

Cell size, cell shape, and cell arrangement.

What is bacterial morphology?

The shape of bacterial cells.

What is bacterial arrangement?

The way bacterial cells are positioned relative to one another.

What is a bacillus?

A rod-shaped bacterial cell.

What is a coccus?

A spherical or round bacterial cell.

What does strepto mean when describing bacterial arrangement?

Cells arranged in chains.

What does a Gram-negative result indicate?

The cells appear pink.

What does a Gram-positive result indicate?

The cells appear purple.

What is a pure culture?

A culture containing only one type of microorganism.

What happens to Gram-positive cells during the decolorization step?

They retain the crystal violet and remain purple.

What happens to Gram-negative cells during the decolorization step?

They lose the crystal violet and can then be stained pink by safranin.

Why do Gram-positive and Gram-negative bacteria stain differently?

Their cell walls have different structures.

Which bacterial cell wall has an outer membrane?

Gram-negative.

Which bacterial cell wall lacks an outer membrane?

Gram-positive.

Which Gram reaction is purple?

Gram-positive.

Which Gram reaction is pink?

Gram-negative.

What is the correct order of the Gram stain procedure?

Crystal violet → Gram's iodine → ethyl alcohol (decolorizer) → safranin.