Lab Quiz #3: Differential & Selective Media

Question 1

A media is designed that allows only staphylococci to grow. In addition, S. aureus colonies have a yellow halo around them and other staphylococci appear white. This type of media is ___.
A. differential only
B. a reducing media
C. selective only
D. both selective and differential
E. enriched

Answer 1

D. both selective and differential

Question 2

A selective growth medium
A. is cultured anaerobically
B. accentuates differences between the growing bacteria
C. allows all bacteria to grow
D. allows no bacteria to grow
E. allows only certain bacteria to grow

Answer 2

E. allows only certain bacteria to grow

Question 3

Mannitol salt agar is selective for which bacterial genus?
A. Escherichia
B. Salmonella
C. Neisseria
D. Staphylococcus
E. Streptococcus

Answer 3

D. Staphylococcus

Question 4

Media that change color as a result of the biochemical activity of growing bacteria
A. contain a colorless reagent that breaks down
B. usually contains a pH indicator
C. usually contains blood
D. are always selective media
E. usually require the addition of various reagents before the color is evident

Answer 4

B. usually contain a pH indicator

Question 5

Media that have additional components for enrichment are used to grow organisms that are
A. ubiquitous
B. Gram negative
C. fastidious
D. halotolerant
E. anaerobes

Answer 5

C. fastidious

Question 6

Some organisms growing on blood agar show a visible clearing of the red color. This is due to blood cells in the media
A. swelling due to the hypertonic nature of blood agar
B. migrating away from the growth of the organism
C. bursting, releasing hemoglobin
D. swelling due to the hypotonic nature of blood agar

Answer 6

C. bursting, releasing hemoglobin

Question 7

Which medium is both selective and differential, and contains lactose as well as the pH indicator neutral red?
A. mannitol salt agar (MSA)
B. blood agar
C. chocolate agar
D. MacConkey agar (MAC)
E. eosin methylene blue agar (EMB)

Answer 7

D. MacConkey agar (MAC)

Question 8

Which medium is both selective and differential, contains a high percentage of salts and inhibits the growth of organisms besides Staphylococcus?
A. chocolate agar
B. mannitol salt agar (MSA)
C. eosin methylene blue agar (EMB)
D. blood agar
E. MacConkey agar (MAC)

Answer 8

B. mannitol salt agar (MSA)

Question 9

Which term is used when a microorganism growing on blood agar incompletely lyse erythrocytes in the surrounding medium?
A. alpha hemolysis
B. beta hemolysis
C. gamma hemolysis
D. no hemolysis
E. delta hemolysis

Answer 9

A. alpha hemolysis

Question 10

Which type of medium is able to distinguish different species or types of microorganisms based on an observable change in the colonies or in the medium?
A. reducing
B. selective
C. enriched
D. enumeration
E. differential

Answer 10

E. differential