Metabolic Activities

Question 1

Starch digestion

Answer 1

• Tests for amylase
• Amylase turns starch into sugars
• Iodine turns stach black, but not sugar
• Reagent: Iodine

Question 2

Starch digestion positive

Answer 2

Clearing around streak

Question 3

Starch digestion negative

Answer 3

Entire plate is black - no clearing

Question 4

Milk Agar Plate

Answer 4

• Casein digestion
• Tests for caseinase
• Caseinase converts casein into amino acids
• No reagent

Question 5

Milk Agar Positive

Answer 5

Clearing around streak

Question 6

Milk Agar Negative

Answer 6

No clearing around streak

Question 7

TSA Plate

Answer 7

• Catalase

- Oxidase Production

Question 8

Catalase

Answer 8

• TSA Plate
• Tests for presence of catalase
• Reagent: H2O2
• Catalase converts H202 to water and oxygen gas

Question 9

Catalase Positive

Answer 9

Bubbles after adding peroxide

Question 10

Catalase Negative

Answer 10

No bubbles after adding peroxide

Question 11

Oxidase Production

Answer 11

• TSA Plate
• Tests for presence of cytochrome oxidase
• Cytochrome oxidase is last enzyme in ETS
• Reagent: on swab

Question 12

Oxidase Production Positive

Answer 12

Dark Purple (pink = weak positive) on swab

Question 13

Oxidase Production Negative

Answer 13

No color change on swab

Question 14

SIM Media

Answer 14

• H2S Production

- Indole Production

Question 15

H2S Production

Answer 15

• SIM Media
• Tests for cysteine desulfurase
• Cysteine desulfurase converts cysteine into pyruvate by removing H2S
• Reagent: iron in medium

Question 16

H2S Production Positive

Answer 16

Black precipitate

Question 17

H2S Production Negative

Answer 17

No black precipitate

Question 18

Indole Production

Answer 18

• SIM Media
• Tests for tryptophanase
• Tryptophanase converts tryptophan into indole
• Reagent: Kovac’s reagent

Question 19

Indole Production Positive

Answer 19

Red layer on tope of broth

Question 20

Indole Production Negative

Answer 20

No color change

Question 21

Citrate Utilization

Answer 21

• Tests for ability to use citrate as a carbon source
• No other carbon source (sugar) available in medium
• Reagent: ammonium ions and brom thymol blue in medium (pH indicator)

Question 22

Citrate Utilization Positive

Answer 22

Bacteria will grow

Usually turns deep blue color

Question 23

Citrate Utilization Negative

Answer 23

Bacteria do not grow
No color change
(However bacteria may grow without changing color)

Question 24

Urea Broth

Answer 24

• Tests for urease
• Urease converts urea into ammonia
• Reagent: Phenol red in medium

Question 25

Urea Broth Positive

Answer 25

Cerise or hot pink

Question 26

Urea Broth Negative

Answer 26

Any color besides cerise or hot pink

Question 27

Nitrate Broth

Answer 27

- Tests for nitrate reductase - Nitrate reductase converts nitrate into nitrite - Reagent: Nitrate 1 (Sulfanilic acid) and Nitrate 2 (dimethyl-a-napthalamine) - Secondary reagent Zinc (to confirm negative)

Question 28

Nitrate Broth Positive

Answer 28

-Red color after adding reagents OR -No color change, then add zinc > still no color change

Question 29

Nitrate Broth Negative

Answer 29

No color change, then red after adding zinc

Question 30

Nitrate Broth Explanation

Answer 30

Sometimes instead of converting Nitrate to Nitrite nitrate reductase converts it to "something else," so there is no color change to red (no nitrite present). However nitrate reductase is still present. To confirm a negative, add zinc to tube. Zn reacts with nitrate to produce a red color. If NR was present, there will be no color change after adding zinc because the nitrate was converted to "something else"

Question 31

MRVP Broth

Answer 31

- Methyl Red | - Voges-Proskauer

Question 32

Methyl Red

Answer 32

- Tests for dextrose fermentation | - Reagent: methyl red

Question 33

Methyl Red Positive

Answer 33

Red color

Question 34

Methyl Red Negative

Answer 34

No red color

Question 35

Voges-Proskauer

Answer 35

- Tests for Butanediol fermentation | - Reagent: Barritt's Solution A (a-naphtol) and B (KOH)

Question 36

Voges-Proskauer Positive

Answer 36

Pink to red color

Question 37

Voges-Proskauer Negative

Answer 37

No pink or red

Question 38

Fermentation Tests

Answer 38

- Tests for specific enzymes that can ferment each sugar - Dextrose - Sucrose - Mannitol - Lactose - Reagent: Phenol Red - Durham Tube to collect gas

Question 39

Durham Tube

Answer 39

Upside down tube in test tube | Collects gas created during rxn

Question 40

Fermentation Test Possible Results

Answer 40

+ acid + gas + acid - gas - acid - gas

Question 41

Fermentation Test Positive

Answer 41

Acid: Yellow Gas: Bubble in Durham tube

Question 42

Fermentation Test Negative

Answer 42

Acid: Red (does not turn yellow) Gas: No bubble in Durham tube

Question 43

IMVC Tests

Answer 43

Indole Production Methyl Red Voges-Proskauer Citrate Utilization -Used to differentiate between E. coli and E. aerogenes (very morphologically similar) -E. coli is positive for I and M, negative for V and C -E aerogenes is opposite