Differential, selective, and enriched media

Question 1

General purpose media

Answer 1

-indicates the media meets the nutritional requirements of most bacteria species, therefore supports the growth of majority of the bacteria species you attempt to culture

Question 2

What media do we use in lab?

Answer 2

-general- purpose complex media, more specifically trypticase soy agar and broth

Question 3

selective media

Answer 3

-used to isolate specific groups of bacteria
-contains substances that inhibit the growth of some bacteria species while promoting growth of others

Question 4

Mannitol salt agar (MSA)

Answer 4

-contains a high salt concentration (7.5% NaCl) which is inhibitory to the growth of almost all bacteria except for staphylococci (S. aureus, or S. epidermidis)
-contains sugar mannitol and specific pH indicators (phenol red)
-promotes the growth of bacteria that can tolerate high salt concentrations (SELECTIVE)
-allows you to determine if a bacteria species ferments mannnitol (DIFFERENTIAL) (changes color)
-when mannitol is fermented acid is produced which lowers the pH
- pH is 7.4-8.4 phenol red is red
- pH is less than 6.8 phenol red is yellow

Question 5

MacConkey agar

Answer 5

-contains bile salts and crystal violet which inhibit the growth of gram positive microbes thus allowing for isolation of gram negative
-contains sugar lactose and specific pH indicators (natural red)
-its SELECTIVE because the bile salts and crystal violet prevent gram positive bacteria from growing
-its DIFFERENTIAL because neutral red and lactose allow you to tell you what bacteria is based on fermentation
-if the pH of the media is between 6.8-8.0 neutral red is colorless
- if the pH of the media is acidic and less than 6.8, neutral red is wine pink
-if the pH of the media is basic and above 8.0, neutral red is yellow

Question 6

Eosin methylene blue (EMB)

Answer 6

-inhibits the growth of most gram positive bacteria, uses the dye eosin Y and methylene blue which allow gram negative bacteria to grow
- also permits the differentiation between lactose and non-lactose fermenters, and uses dyes eosin and methylene blue which precipitate on the growth’s surface when lactose is fermented
* bacteria that ferment lactose will have colonies that appear metallic green or dark purple
* E.coli will appear metallic green

Question 7

Differential media

Answer 7

-allows you to tell the difference between morphologically and biochemically related groups of bacteria
-contains compounds that produce a distinct change in the appearance of a bacterial colony or the media surrounding the colony

Question 8

fastidious organism

Answer 8

difficult to grow on general purpose media

Question 9

enriched media

Answer 9

-used to promote the growth of fastidious bacteria that grow poorly or not at all on general media
-contains additional biochemicals that are highly nutritious and support the needs of fastidious bacteria
-they are often supplemented with blood, yeast, or serum (plasma)

Question 10

Examples of selective media

Answer 10

-Eosin methylene blue agar
-MacConkey agar
-Mannitol salt agar (MSA) (also differential)

Question 11

What is mannitol salt agar (MSA) used to identify

Answer 11

-species of staphylococcus (S. aureus, and S. epidermis)
-MSA promotes the growth of staphylococcus with high salt, and allows differentiation based on if mannitol is their food source

Question 12

E.coli on mannitol salt agar (MSA)

Answer 12

-unable to grow on media with high salt

Question 13

S. aureus on mannitol salt agar (MSA)

Answer 13

grows in high salt environment and ferments mannitol

Question 14

S. epidermidis on mannitol salt agar (MSA)

Answer 14

grows in high salt environment and does not ferment mannitol

Question 15

Examples of differential media

Answer 15

-blood agar
-MacConkey agar (also selective)
-Eosin Methylene blue
-Mannitol salt agar

Question 16

What is the MacConkey media used to isolate

Answer 16

members of Enterobacteriaceae

Question 17

S. epidermidis on MacConkey agar

Answer 17

gram positive

Question 18

Pseudomonas on MacConkey agar

Answer 18

gram negative and does not ferment lactose

Question 19

E.coli on MacConkey agar

Answer 19

gram negative and ferments lactose

Question 20

What does coliform includes

Answer 20

Escherichia coli and Enterobacter aerogenes

Question 21

S. epidermidis on eosin methylene Blue agar (EMB)

Answer 21

gram positive

Question 22

Pseudomonas on eosin methylene blue agar (EMB)

Answer 22

gram negative and does not ferment lactose

Question 23

E.coli on eosin methylene blue agar (EMB)

Answer 23

gram negative and ferments lactose

Question 24

Blood agar plates (BAP)

Answer 24

-contain TSA to which 5% sheep blood has been added for enrichment ingredients for fastidious organisms
-permits demonstration of hemolytic properties of some microorganisms, particularly streptococci
-its DIFFERENTIAL because it allows you to determine the type or varying degree of hemolysis of a bacteria species
-these plates in lab show alpha, beta, and gamma hemolytic

Question 25

hemolytic

Answer 25

bacteria that contain hemolysins (endotoxins) that break down red blood cells

Question 26

alpha hemolytic bacteria

Answer 26

partial breakdown of RBC (a green-brown color colonies)

Question 27

Beta hemolytic bacteria

Answer 27

complete breakdown of RBC (clearing media around growth)

Question 28

Gamma hemolytic bacteria

Answer 28

no breakdown of RBC (no change in media)

Question 29

Mannitol salt agar (MSA) turns what color in the presence of acid?

Answer 29

yellow