Test for Streptococcus

Question 1

Presumptive test for S. pyogenes

Answer 1

Bacitracin susceptibility, PYR test

Question 2

Principle of Bacitracin susceptibility test

Answer 2

Inoculate organism in media and place a 0.04 units Taxo A disk (Bacitracin)

Question 3

Medium for Bacitracin susceptibility test

Answer 3

Supported media or BAP

Question 4

Incubation for Bacitracin susceptibility test

Answer 4

35-37°C, 18-24 hours, 5-10% CO2

Question 5

Positive QC for Bacitracin susceptibility

Answer 5

Zone of inhibition >10 mm (S. pyogenes, Micrococcus luteus)

Question 6

Negative QC for Bacitracin susceptibility

Answer 6

No zone of inhibition (S. agalactiae, S. aureus)

Question 7

Principle of PYR test

Answer 7

L-Pyrrolidonyl-β-naphthylamide + L-pyrrolidonyl arylamidase → β-naphthylamine (detected by indicator)

Question 8

Medium for PYR test

Answer 8

Filter paper PYR disk

Question 9

Reagent/Indicator for PYR test

Answer 9

N,N-methylamino-Cinnamaldehyde

Question 10

Incubation for PYR test

Answer 10

22-25°C, 2 minutes

Question 11

Positive QC for PYR test

Answer 11

Bright red color within 5 minutes (E. faecalis, S. pyogenes)

Question 12

Negative QC for PYR test

Answer 12

No color change (S. agalactiae)

Question 13

Presumptive test for Enterococci and S. bovis

Answer 13

Bile esculin hydrolysis

Question 14

Principle of bile esculin hydrolysis test

Answer 14

Organisms grow in 40% bile and hydrolyze it to esculetin

Question 15

Medium for bile esculin hydrolysis test

Answer 15

Bile esculin slant with ferric ammonium citrate (iron)

Question 16

Incubation for bile esculin hydrolysis test

Answer 16

35-37°C, 48 hours

Question 17

Positive QC for bile esculin hydrolysis

Answer 17

Growth + black precipitate (E. faecalis)

Question 18

Negative QC for bile esculin hydrolysis

Answer 18

Growth but no blackening (E. coli) or no growth and no blackening (S. pyogenes)

Question 19

Presumptive test for S. pneumoniae

Answer 19

Optochin (P disk) susceptibility test, Bile solubility test

Question 20

Principle of Optochin (P disk) test

Answer 20

Ethylhydrocupreine hydrochloride (Taxo P disk) inhibits S. pneumoniae growth

Question 21

Medium and setup for Optochin test

Answer 21

Organism on BAP + P disk, incubate at 35°C, 18-24 hours, 5% CO2

Question 22

Positive result for Optochin test

Answer 22

Zone of inhibition >14 mm (S. pneumoniae)

Question 23

Negative result for Optochin test

Answer 23

Zone of inhibition <14 mm (S. pyogenes)

Question 24

Principle of Bile solubility test

Answer 24

S. pneumoniae’s amidase enzyme lyses its colonies in the presence of bile salts

Question 25

Setup for Bile solubility test

Answer 25

Colony on BAP or broth culture + 10% Sodium deoxycholate, incubate at 35-37°C for 30 minutes

Question 26

Positive result for Bile solubility test

Answer 26

Colony disintegration on agar or broth culture becomes clear (S. pneumoniae)

Question 27

Negative result for Bile solubility test

Answer 27

Colonies remain intact or broth remains turbid (E. faecalis, Viridans)

Question 28

Test that differentiates Group B Streptococcus from others

Answer 28

CAMP test

Question 29

Factor that enhances beta-lysin hemolysis of S. aureus

Answer 29

CAMP factor

Question 30

Positive result for CAMP test

Answer 30

Arrowhead hemolysis (S. agalactiae)

Question 31

Negative result for CAMP test

Answer 31

No enhanced hemolysis/arrowhead (S. pyogenes)

Question 32

Medium and incubation for CAMP test

Answer 32

BAP at 35-37°C for 16-18 hours

Question 33

Test for presumptive identification of S. agalactiae and others

Answer 33

Hippurate hydrolysis test

Question 34

Reaction in Hippurate hydrolysis test

Answer 34

Hippurate + hippuricase → glycine and benzoic acid

Question 35

Positive result for Hippurate hydrolysis test

Answer 35

Deep purple (S. agalactiae)

Question 36

Negative result for Hippurate hydrolysis test

Answer 36

Colorless or yellow-pink (S. pyogenes)

Question 37

Incubation for Hippurate hydrolysis test

Answer 37

35°C for 2 hours

Question 38

Test for Enterococci identification

Answer 38

LAP test

Question 39

Reaction in LAP test

Answer 39

Leucine-β-naphthylamine + leucine aminopeptidase → β-naphthylamine

Question 40

Positive result for LAP test

Answer 40

Red (E. faecalis)

Question 41

Negative result for LAP test

Answer 41

Yellow/No color change (Aerococcus viridans)

Question 42

Incubation for LAP test

Answer 42

22-25°C for 5 minutes

Question 43

Test for differentiation between Enterococcus faecalis and Enterococcus faecium

Answer 43

Pyruvate test

Question 44

Reaction in Pyruvate test

Answer 44

Ability to use Pyruvate to form acids

Question 45

Positive result for Pyruvate test

Answer 45

Yellow (E. faecalis)

Question 46

Negative result for Pyruvate test

Answer 46

No change or Yellow-Green/Weak (S. gallolyticus)

Question 47

Incubation for Pyruvate test

Answer 47

35-37°C for 24-48 hours

Question 48

Test for Enterococci's ability to withstand high salinity

Answer 48

Salt Tolerance test

Question 49

Medium for Salt Tolerance test

Answer 49

Heart infusion broth + 6.5% NaCl

Question 50

Positive result for Salt Tolerance test

Answer 50

Growth, Yellow (E. faecalis)

Question 51

Negative result for Salt Tolerance test

Answer 51

Little/no growth (S. gallolyticus)

Question 52

Incubation for Salt Tolerance test

Answer 52

35-37°C for 24-48 hours