Staining

Question 1

Bacteria have a thick cell wall made of the

Answer 1

polysaccharide peptidoglycan

Question 2

Some bacteria have a thick peptidoglycan layer around their cell membrane

Answer 2

gram-positive

Question 3

Others have a thin peptidoglycan layer surrounded by a lipid containing layer

Answer 3

gram-negative bacteria

Question 4

Gram staining (what are the steps)

Answer 4

-Primary staining with crystal violet
-Application of a mordant to bind the dye
-Rinse with a decolorizing agent to release unbound dye
-Counterstaining with safranin

Question 5

What occurs when a bacteria contains a lipid layer ?

Answer 5

Bacteria containing a lipid layer will not bind the crystal violet dye, and will be counterstained.

Question 6

Gram-positive bacteria retain ______ and will be _____

Answer 6

• crystal violet
  -purple

Question 7

Gram-negative bacteria will be counterstained with _______ and will be______

Answer 7

-saranin
-pink

Question 8

When is negative staining used?

Answer 8

Negative staining is used to study bacteria that are difficult to stain or cannot be heat fixed.

Question 9

Does negative staining stain the bacteria or background and what dye is used? Are these dyes basic or acidic?

Answer 9

It stains the background so that the bacteria can be more easily seen.
India Ink or Nigrosin are used. They are acidic stains.

Question 10

Since the surface of most bacterial cells is negatively charged, what happens to the cell surface and glass during negative staining?

Answer 10

Since the surface of most bacterial cells is negatively charged, the cell surface repels the stain, but the glass does not.

Question 11

What is acid fast staining primarily used to stain and how does this happen?

Answer 11

• Used to stain Mycobacterium
• Heat allows the carbol fuchsin stain to pass through the waxy mycolic acid in the cell wall.
• Once removed from heat, an acid alcohol decolorizer is applied. The stain will be released from all bacteria EXCEPT Mycobacterium
  Other cells can then be counterstained with methylene blue or another simple stain

Question 12

In acid-fast staining, mybacteria appear_____ and other cells appear

Answer 12

• pink
  -blue

Question 13

What are bacterial endospores?

Answer 13

Bacterial endosporesare a dormant state some bacteria can produce under highly unfavorable conditions

Question 14

What dye is used for staining bacterial endospore and what happens to the vegetative endospores?

Answer 14

Malachite green and heat are used to drive stain into endospores so that it does not wash out.

Vegetative (nonspore) cells readily lose the stain during water rinse

Question 15

What happens when counterstaining with safranin during endospore staining?

Answer 15

Counterstain of safranin stains the vegetative cells pink to provide contrast.

Question 16

What color does the endospores appear vs the vegetative cells

Answer 16

• endospores= green
  -vegetative (non-spore)- cells appear pink