Exercise 3: Microbial Enzymatic Assay

Question 1

What does the catalase test detect?

Answer 1

Presence of catalase enzyme (breaks H₂O₂ into water + oxygen)

Question 2

What is indicated by bubbling in a catalase test?

Answer 2

Positive result (O₂ released)

Question 3

What does the oxidase test detect?

Answer 3

cytochrome c oxidase

Question 4

What color indicates a positive oxidase test?

Answer 4

Dark-blue or maroon

Question 5

What does a positive methyl red test mean?

Answer 5

Mixed acid fermentation (pH ≤ 4.2, red color)

Question 6

What is detected in a Voges-Proskauer (VP) test?

Answer 6

Production of acetoin

Question 7

What does a positive VP test show?

Answer 7

Red color after adding reagents

Question 8

What does Simmon’s Citrate test assess?

Answer 8

Use of citrate as sole carbon source

Question 9

What indicates a positive citrate test?

Answer 9

Blue color (alkaline pH)

Question 10

What does the malonate test determine?

Answer 10

Use of malonate as sole carbon source

Question 11

What color shows a positive malonate test?

Answer 11

Blue (alkaline shift)

Question 12

What enzyme hydrolyzes starch?

Answer 12

Alpha-amylase

Question 13

What indicates starch hydrolysis on agar?

Answer 13

Clear zone after iodine

Question 14

What does gluconate oxidation test detect?

Answer 14

Production of 2-ketogluconate

Question 15

What reagent is used in gluconate oxidation test?

Answer 15

Benedict’s reagent

Question 16

What indicates positive Benedict’s test?

Answer 16

Orange/yellow precipitate (Cu₂O)

Question 17

What enzyme breaks down gelatin?

Answer 17

Gelatinase

Question 18

What indicates a positive gelatin hydrolysis test?

Answer 18

Medium remains liquid when cold

Question 19

What enzyme breaks down lipids?

Answer 19

Lipase

Question 20

What indicates lipid hydrolysis in Sierra’s medium?

Answer 20

Opaque zone (calcium oleate)

Question 21

What enzyme does the urea test detect?

Answer 21

Urease

Question 22

What is a positive urease result?

Answer 22

Pink (alkaline pH due to ammonia)

Question 23

What does indole test detect?

Answer 23

Production of indole from tryptophan

Question 24

What reagent is used in indole test?

Answer 24

Kovac’s reagent

Question 25

What indicates positive indole test?

Answer 25

Red layer on surface

Question 26

What enzyme does phenylalanine deamination test detect?

Answer 26

Phenylalanine deaminase

Question 27

What color shows positive phenylalanine deamination?

Answer 27

Green after ferric chloride

Question 28

What does lysine decarboxylation test detect?

Answer 28

Enzyme lysine decarboxylase

Question 29

What color change indicates positive lysine test?

Answer 29

Yellow to purple (alkaline shift)

Question 30

What enzyme does nitrate reduction test detect?

Answer 30

Nitrate reductase

Question 31

What enzyme produces hydrogen sulfide (H₂S)?

Answer 31

Cysteine desulfurase

Question 32

What indicates positive H₂S test?

Answer 32

Black precipitate in medium

Question 33

What medium is used in the Catalase Test?

Answer 33

Nutrient Agar (Agar)

Question 34

What medium is used in the Oxidase Test?

Answer 34

Nutrient Agar (NA); colonies are transferred to oxidase reagent-moistened filter paper.

Question 35

What medium is used in the Methyl Red Test?

Answer 35

Nitrate Broth Glucose (NBG)

Question 36

What medium is used in the VP Test?

Answer 36

Nitrate Broth Glucose (NBG)

Question 37

What medium is used in the Citrate Utilization Test?

Answer 37

Simmons Citrate Agar (SCA)

Question 38

What medium is used in the Malonate Utilization Test?

Answer 38

Malonate Broth (MB)

Question 39

What medium is used in the Starch Hydrolysis Test?

Answer 39

Starch Agar Medium

Question 40

What medium is used in the Gelatin Liquefaction Test?

Answer 40

Nutrient Gelatin (NG)

Question 41

What medium is used in the Indole Production Test?

Answer 41

Tryptone Broth

Question 42

What medium is used in the Nitrate Reduction Test?

Answer 42

Nitrate Broth with Durham Tube (NBN)