Lab Final

Question 1

Micrococcus Luteus

Answer 1

Gram + cocci; No growth on HE and EMB agar; Clusters

Question 2

Spores form on

Answer 2

Gram + rods

Question 3

Spores appear

Answer 3

clear or light blue

Question 4

Staphylococcus epidermidis

Answer 4

Gram + cocci; No growth on EMB agar; grape like clusters

Question 5

Escherichia coli

Answer 5

Gram - rod; Lactose fermenter on HE and EMB agar; coliform

Question 6

Bacillus subtilis

Answer 6

gram + rod; spores

Question 7

1. Crystal violet

Answer 7

1-2 minutes

Question 8

2. Gram’s Iodine

Answer 8

1 minute

Question 9

3. Acetone-alcohol

Answer 9

1-2 seconds

Question 10

4. Safranin

Answer 10

1-2 minutes

Question 11

The primary stain

Answer 11

Crystal violet

Question 12

The mordant

Answer 12

Gram’s iodine, a reagent that sets the dye in the tissue or cell

Question 13

The decolorizer

Answer 13

Acetone-alcohol

Question 14

The counterstain

Answer 14

Safranin

Question 15

Saccharomyces cerevisiae

Answer 15

Gram + cocci; buds

Question 16

EMB agar

Answer 16

Eosin Methylene Blue Agar (Red)

Question 17

HE agar

Answer 17

Hektoen Enteric Agar (Green)

Question 18

EMB agar is differential because

Answer 18

it allows fermentation (color change of the agar)

Question 19

EMB agar is selective because

Answer 19

gram + bacteria cannot grow there. It is selective for gram - organisms.

Question 20

HE agar is slective because

Answer 20

Gram + organisms cannot grow there. It is selective for gram - organisms.

Question 21

Metallic green on EMB agar means

Answer 21

the organism is a lactose fermenter

Question 22

HE fementating carbohydrates

Answer 22

lactose, sucrose, and salicin

Question 23

Why is the immersion oil added to the microscope?

Answer 23

the oil acts as an additional lens in the system and prevents the loss of necessary light rays.

Question 24

simple stain

Answer 24

-The bacteria is stained with one dye and subsequently, the bacteria will all be the same color

Question 25

Gram stain is based on

Answer 25

cell wall composition

Question 26

Why you should allow the smear to air dry? why you cannot use heat to do this?

Answer 26

• because the slide is allowed to sit until it has no longer appears moist
• If heat is used to speed up the drying process, the cell wall of the organisms may be distorted or rupture and release the cyrstal violet dye when it should retain it

Question 27

By adding the de-colorizer after the mordant, what color would you think the cells would be?

Answer 27

The gram positive cell would be PURPLE.

The gram negative cell would be CLEAR.

Question 28

What is the difference between gram positive and gram negative?

Answer 28

• Gram negative have an outer membrane, and they also have a thin peptidoglycan. Gram positive on the other hand, do not have an outer membrane, and have a very thick peptidoglycan
• The Gram-positive cells have thick walls, and they will retain the purple crystal violet stain if decolorization was carried out correctly. The Gram-negative cells will be decolorized and are colorless. Watch the video to review the effect of decolorization on both types of cells.

Question 29

In cells, the gram reaction depends on what?

Answer 29

Their gram reaction depends on their cell wall composition.