Stains

Question 1

What is an auxochrome?

Answer 1

auxochrome

• component of dye that does not produce color but gives the dye its acidic or basic (electron donor or acceptor) properties.
• Examples are electron donors or acceptors that extend the conjugated system of the chromophore.
  
  • NH2
  • OH
  • OCH3
  • I
  • Br
  • Cl

Question 2

What is a chromophore?

Answer 2

Chromophore

• component of dye that imparts color to the dye molecule
• these are usually resonant structures that can absorb light and UV over certain wavelengths.
  
  • Transmission of the remainder of the spectrum gives them their characteristic colors.

Question 3

Circle the auxochrome groups in the following stains:

Answer 3

Question 4

What is the point of Simple staining?

Answer 4

• Simple staining is merely the use of a dye to increase the contrast of cells for microscopy.
• As an example, a simple stain would be used to detect the presence of bacteria in some natural material such as urine or water.
• It must be remembered that a simple stain alone is not useful as an identification tool.

Question 5

What is a mordant?

Answer 5

mordant

• a chemical compound that reacts with the stain to form an insoluble, colored precipitate.

Question 6

• We most often use ________ (anionic/cationic) stains to examine bacteria. as ________ (anionic/cationic) stains are much less common and are used only for special purposes.

Answer 6

• We most often use cationic stains to examine bacteria. as anionic stains are much less common and are used only for special purposes.

Question 7

What is the purpose of this stain:

Coomassie blue

Answer 7

Coomassie blue

• stains proteins a brilliant blue
• Can be used to estimate the amount of protein in a solution (Bradford Assay)

Question 8

What is the purpose of this stain:

Crystal violet

Answer 8

Crystal violet

• stains cell walls purple when combined with a mordant.
• This stain is used in Gram staining

Question 9

What is the purpose of this stain:

Malachite green

Answer 9

Malachite green

• a blue-green counterstain to safranin
• used to stain spores.

Question 10

What is the purpose of this stain:

Methylene blue

Answer 10

Methylene blue

• stains animal cells to make nuclei more visible.

Question 11

What is the purpose of this stain:

Safranin

Answer 11

Safranin

• a simple stain to visualize bacterial cells.

Question 12

What are the differences between these types of stains?

• simple staining
• negative staining
• differential staining
• background staining
• capsule staining

Question 13

What is the purpose of this stain:

Congo Red

Answer 13

• Capsules can be observed by negative stains or by combining a negative stain and a simple stain.
• “Negative stains” such as India ink, nigrosin and Congo Red stain the background but not the bacterial cells or capsules.

Question 14

What is Maneval’s solution?

Answer 14

Maneval’s solution?

• The staining method in which the outer layer of cell wall (ie capsule) is stained is called capsule staining by Maneval’s method.
• It is a counterstain, allowing for congo red’s color to change from blue to red in basic to acidic conditions.

Question 15

What is the point of steaming during spore staining?

Answer 15

• Endospores are impervious to most ordinary stains.
• Malachite green is placed on a bacterial smear and heat (form the steam) is used to drive the dye into the spores.