Module 10

Question 1

QC for bacitracin susceptibility

Answer 1

Sensitive (susceptible) control: Group A Streptococcus (S. pyogenes)
Resistant control: Group B, C, F or G Streptococcus (S. agalactiae)

Question 2

PYR test

Answer 2

Colorimetric test for the enzyme L-pyrrolidone aminopeptidase
Used to differentiate species of Group D Streptococci (Enterococcus vs. Non Enterococcus)
presumptive ID test for Group A Streptococcus
Red = positive
Colorless = negative

Question 3

PYR test QC

Answer 3

Positive: Group D Enterococcus/Group A Streptococcus
Negative: Group D Non Enterococcus (S. bovis), other beta hemolytic Streptococci (Groups B, C, F, and G)

Question 4

Reagent used for colour development in the PYR test

Answer 4

Cinnamaldehyde

Question 5

In a positive esculin hydrolysis test, esculin is hydrolyzed to:

Answer 5

Esculetin and glucose

Question 6

End product for the rapid hippurate hydrolysis test

Answer 6

Glycine

Question 7

Using old colonies for a bile solubility test can cause:

Answer 7

False insoluble results

Question 8

Strain of Staphylococcus aureus used for CAMP testing

Answer 8

ATCC 25923

Question 9

Reagents for the bile solubility test

Answer 9

Sodium taurocholate or sodium deoxycholate (10% solution)

Question 10

Recommended atmosphere for incubating blood agar plates inoculated with throat swabs

Answer 10

Anaerobic

Question 11

For ID of Strep species, why do we use a blood agar base free of fermentable carbohydrates?

Answer 11

Streptolysin S (present in some beta-hemolytic Streptococci) may be altered by acid produced by carbohydrate fermentation, losing its hemolytic effect. As a result, beta-hemolytic Streptococci may not be worked up properly

Question 12

Ideal atmosphere for incubation of Streptococcus and why

Answer 12

Anaerobic conditions
Streptolysin O (present in some beta-hemolytic Streptococci) is destroyed by oxygen. Exposure to oxygen would affect the hemolysis of some Streptococci

Question 13

Bacitracin susceptibility

Answer 13

Used for presumptive ID of Group A Strep
Bacitracin or Taxos A disc is added to original throat plate or pure culture of beta-hemolytic Strep, incubate overnight at 35C

Question 14

CAMP test is used for presumptive ID of:

Answer 14

Group B Streptococcus

Question 15

Media in CAMP test

Answer 15

Sheep or bovine blood cells used
Thin plates (1.5mm) warmed to room temp with a dry surface

Question 16

CAMP test controls

Answer 16

Positive: Group B Strep (S. agalactiae)
Negative: Group A Strep (S. pyogenes)

Question 17

Reagent in rapid hippurate hydrolysis test

Answer 17

Ninhydrin

Question 18

Rapid hippurate hydrolysis test is used for presumptive ID of:

Answer 18

Group B Streptococcus

Question 19

Incubation for rapid hippurate hydrolysis test

Answer 19

2-4hrs at 35C, then 10min at 35C after reagent is added

Question 20

Rapid hippurate hydrolysis controls

Answer 20

Positive: Group B Strep (S. agalactiae) or Campylobacter jejuni
Negative: Group A Strep (S. pyogenes) or Campylobacter coli

Question 21

False positives in rapid hippurate hydrolysis test

Answer 21

Amino acids from peptones in media

Contamination from mixed cultures

Question 22

Bile esculin test controls

Answer 22

Positive: Group D (Enterococcus faecalis)
Negative: Group B (S. agalactiae), Group A Strep, S. pneumoniae, S. viridans

Question 23

Bile solubility test controls

Answer 23

Bile soluble control: S. pneumoniae

Bile insoluble control: S. viridans