Common Microbial Biochemical Tests

Question 1

CHO breakdown

Answer 1

Lactose fermenters vs NLF

E.coli vs. Salmonella

Question 2

Catalase production - form bubbles

Answer 2

Staph ( catalase positive) vs Strep (catalase neg)

Question 3

Citrate utilization

Answer 3

Ability to use citrate

Klebsiella pneumoniae is citrate positive

Question 4

Coagulase test

Answer 4

Staph aureus vs less pathogenic staph

Question 5

Decarboxylase and Deaminase

Answer 5

Form colored products as AA change pH

Gram neg rods

Question 6

Hydrogen sulfide

Answer 6

Between gram pos rods

Black color of sulfide salts with heavy metals i.e Fe

Question 7

Indole test

Answer 7

Ability to produce indole from tryptophan - Red dye

Proteus vulgaris is indole positive

Question 8

Nitrate reduction

Answer 8

Detect presence of UTI

Question 9

O- nitrophenyl - B- D- galactoside breakdown

Answer 9

ONPG pos and Lactose neg : have B- galactoside to ferment lactose but no permease for lactose to enter the cell

Question 10

Oxidase production (detects cytochrome-oxidase complex)

Answer 10

P.aueruginosa ( oxidase +) E.coli (oxidase -)

Question 11

Proteinase production

Answer 11

P.aeruginosa and S.aureus are positive

Question 12

Urease production (inc pH in medium)

Answer 12

Differentiates P.vulgaris from other enteric rods

Question 13

Voges-Proskauer test (detects acetoin

Answer 13

Differentiates among enteric rods

Question 14

Positive urease

Answer 14

Pink

Question 15

Positive CHO fermentation test

Answer 15

Yellow

Question 16

Positive indole

Answer 16

Pink