SELECTIVE, DIFFERENTIAL, AND ENRICHED MEDIA

Question 1

What material is the bacteria grown? (Think where it’s put when it’s incubating)

Answer 1

culture medium

Question 2

If chemical constituents are known in the medium, what are they called?

Answer 2

chemically defined medium

Question 3

If the microorganism has specific requirements because of their stringent nutritional requirements, what is it called?

Answer 3

Fastidious organism

Question 4

What medium is most used in microbiology?

Answer 4

Nutrient broth/agar

Question 5

What is the nutrient broth/agar medium that supports the growth of many organisms called?

Answer 5

all purpose or general-purpose medium

Question 6

T/F
If a solid medium is desired, agar may be added to the broth medium.

Answer 6

True

Question 7

T/F:
Agar goes into solution or melts when heated to nearly 100C and remains liquid until cooled about 43C

Answer 7

True

Question 8

To cause liquiefaction, it has to be like gelatin.

Answer 8

False, unlike gelatin, once solidified it must be reheated to approx. 100C

Question 9

What is selective media?

Answer 9

Selective media contains specific chemicals which do not affect the growth of the organism you wish to isolate but will discourage the growth of other groups of microorganisms

Question 10

Does the bacterias in selective media lack a cytochrome system? Why?

Answer 10

Yes these organisms lack cytochrome system and are unaffected by the sodium azide that binds tightly to the iron preventing growth.

Question 11

What is differential media?

Answer 11

Differential media contains dyes or chemicals which allow the observer to distinguish between types of bacterial colonies that have developed after incubation

Question 12

What would be an example of differential media? Why?

Answer 12

Eosin Methylene blue agar (EMB), it can also be selective since this medium contains lactose as energy source

Question 13

What is Enriched media?

Answer 13

microorganisms that require specific nutrients

Question 14

What broth cultures were used in the selective, differential, and enriched media experiment?

Answer 14

• Escherichia coli
• Enterobacter aerogenes
• Staphylococcus epidermidis
• Enterococcus faecalis (caution level 2 pathogen)

Question 15

What are the agar plates used in selective, differential, enriched media?

Answer 15

• Tryptic Soy Agar (TSA)
• EMB Agar
• KF streptococcal agar

Question 16

Was there any growth in the TSA? EMB? KF?

Answer 16

TSA: yes for all broth cultures (clear and white)
EMB : moderate to none (black and clear)
KF : none (spots or black)

Question 17

What is the difference between differential and selective media?

Answer 17

differential - used to distinguish one organism from another

selective - allows for the growth of specific organisms

Question 18

What are the dyes found in EMB agar? Which group of microorganisms do the dyes inhibit?

Answer 18

Eosin Y & Methylene Blue

Eosin Y - responds to changes in pH
Methylene - inhibits the growth of gram positive/negative

Question 19

What type of medium is designed to grow a broad range of genera? How does this differ from enriched media?

Answer 19

Genera purpose media:
- allows only the growth of a particular type of microorganism

Enriched media:
- contains all nutrients required for growth