Laboratory Exercise 3 Gram Stain

Question 1

This stain allows for differentiation of bacteria into 2 principle distinct groups: Gram-negative and Gram-positive

Answer 1

Gram Stain

Question 2

Gram-positive vs Gram-negative cell wall composition and structure

Answer 2

Gram positive - thick peptidoglycan with teichoic acid strands inserted, cell membrane
Gram-negative - lipopolysaccharide, outer membrane, thin peptidoglycan, cell mebrane (sandwich)

Question 3

Gram Stain
CLAS

Answer 3

Crystal Violet (1 min) - primary stain
Lugol’s Iodine (1 min) - mordant
Acetone Alcohol (10 sec) - decolorizer
Safranin (30 sec) - counterstain

Question 4

This stain is added to specimen smear

Answer 4

Primary stain
Purple both

Question 5

This makes the dye less soluble so it adheres to the celll walls

Answer 5

Mordant
Purple both

Question 6

This washes away stain from gram negative cell wallsl

Answer 6

Decolorizer
Gram + purple
Gram - colorless

Question 7

This allows dye adherence to gram negative cell walls

Answer 7

Counterstain
Gram + purple
Gram - red

Question 8

Gram positive vs gram negative color

Answer 8

Gram + blue/purple
Gram - pink/red

Question 9

Who discovered a staining method that can divide bacteria into 2 groups based on the abiity of bacteria to retain crystal violet dye during decolorization with alcohol?

Answer 9

Christian Gram

Question 10

Gram + or Gram -?
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa

Answer 10

SA - Gram +
BS - Gram +
PA - Gram -