Lab 3 test

Question 1

Selective media

Answer 1

Used to isolate specific groups of bacteria by incorporating a substance that inhibits the growth of one type of bacteria while permitting growth of another

Question 2

Example of selective media

Answer 2

Phenylethyl alcohol agar (PEA), favors gram + and inhibits gram - species by disrupting DNA synthesis

Question 3

Differential media

Answer 3

Contain chemical compounds that cause bacteria that grow on the medium to change in appearance. It may also result in changes in the surrounding media

Question 4

Organisms that grow on PEA

Answer 4

Gram + (s. aureus, and s. epidermis)

Question 5

7.5% sodium chloride agar selective properties

Answer 5

Promotes growth of halophiles (salt loving microorganisms)

Question 6

What type of bacteria grow well on 7.5% sodium chloride agar

Answer 6

Stapholococcus

Question 7

What is mannitol salt agar made up of

Answer 7

• 7.5% NaCl
• Carbohydrate mannitol
• Phenol red indicator

Question 8

Mannitol salt agar selective properties

Answer 8

Promotes growth of halophiles (salt loving organisms)

Question 9

Mannitol salt agar differential properties

Answer 9

Distinguishing between members of staphylococcus genus, as only some members are able to ferment

Question 10

What color does mannitol turn if it is fermented

Answer 10

From red to yellow (phenol red is an indicator for acid byproducts of fermentation)

Question 11

What can grown on MSA

Answer 11

Only salt tolerant bacteria (contains salt)

Question 12

What does MSA inhibit growth of

Answer 12

Gram -

Question 13

MacConkey agar selective properties

Answer 13

Inhibits gram + species by presence of crystal violent and bile salts, permits growth of gram -

Question 14

Differential properties of MacConkey agar

Answer 14

Lactose in medium distinguishes between enteric lactose fermenting bacteria (pink to red colonies) and non lactose fermenting bacteria (colorless colonies)

Question 15

EMB agar selective properties

Answer 15

Contains eosin and methlyene blue that inhibit growth of many gram + bacteria

Question 16

Differential properties of EMB

Answer 16

Distinguishes between lactose fermenting bacteria and non lactose fermenting bacteria. Fermenting causes color change of colony

Question 17

What color does strong fermentation make EMB

Answer 17

Green

Question 18

What color does weak fermentation make EMB

Answer 18

Pinkish purple

Question 19

What color do non lactose fermenters make EMB

Answer 19

Colorless or at least no darker than media

Question 20

What does Blood agar distinguish between

Answer 20

Distinguishes basteria based on their ability to lyse RBC

Question 21

Possible outcomes on blood agar

Answer 21

Alpha hemolysis
Beta hemolysis
Gamma hemolysis

Question 22

Alpha hemolysis

Answer 22

Partial disruption of RBC. Colony has greenish, brownish coloration

Question 23

Beta hemolysis

Answer 23

Bacteria release emzymes that completely break down the blood cells. Results in media displaying clear halos around colonies

Question 24

Gamma hemolysis

Answer 24

No hemolysis at all

Question 25

Starch

Answer 25

Polysaccharide composed of hundreds of glucose subunits

Question 26

Enzyme that breaks bonds holding glucose subunits together

Answer 26

Amylase

Question 27

What is free glucose used for

Answer 27

Source of energy and carbon

Question 28

Starch test negative color

Answer 28

Orange

Question 29

Starch test positive color

Answer 29

Purple-black

Question 30

Starch hydrolysis petri dish

Answer 30

+ --> amber brown (starch breakdown) | - --> blue black (starch present, no breakdown)

Question 31

What does Skim milk agar test for

Answer 31

Caesin hydrolysis

Question 32

What is the lipid test

Answer 32

Tributyrin agar

Question 33

How to tell if something is positive for lipase production

Answer 33

Clearing surrounding the growth