MICROEX2 Lab Tests

Question 1

Catalase

Answer 1

Differentiates catalase pos and neg bacteria.
POS: bubbles
NEG: no bubbles

Staphylococcus (+)
Micrococcus (+)
Listeria monocytogenes (+)
Vs.
Streptococci (-)

Contamination with blood agar
 Enterococcus psuedocatalase (not true positive)

Question 2

Coagulase (Slide)

Answer 2

Testing for bound coagulase
POS: clumping
NEG: no clumping

Staphylococcus aureus (+)
Vs.
Coag neg Staph (-)

Must confirm w/ tube test

Question 3

Coagulase (Tube)

Answer 3

Testing for free coagulase
POS: clotting
NEG: no clotting

Staphylococcus aureus (+)
Vs.
Coag neg Staph (-)

Question 4

Staph Latex Agg.

Answer 4

Used for the detection of clumping factor and protein A.
POS: large clumps
NEG: no agglutination

S. aureus (+)
vs.
other Staph (-)

Question 5

Microdase

Answer 5

Detects enzyme oxidase
POS: blue/purple color
NEG: no color change

Micrococci (+)
Vs.
Staphylococci (-)

Question 6

Optochin

Answer 6

Optichin lyses pneumoncocci but alpha-strep are resistant
POS: zone > 14 mm
NEG: no zone
EQUIVICOL: zone < 14 mm

Streptococcus pneumoniae (+)
Vs.
Alpha hemolytic strep (-)

Equivicol: confirm w/ bile solubility

Question 7

Bile Solubility

Answer 7

Bile salts lyse pneumococcal colonies
POS: imprint where colony lysed
NEG: intact colonies

Streptococcus pneumoniae (+)
Vs
Alpha hemolytic strep (-)

Old cultures

Question 8

Bile Esculin Salt

Answer 8

Tests for organisms capable of growing in bile salts.
POS: Growth,blackening of slant
NEG: no blackening

Enterococcus (+)
Group D Strep (+)
Listeria monocytogenes (+)
Vs.
Non-group D strep (-)

Question 9

6.5% salt

Answer 9

Tests organisms ability to grow in high salt.
POS: growth (turbidity) w/wo color change
NEG: no growth, no color change

Enterococci (+)
Vs.
Nonenterococci (-)

Question 10

CAMP

Answer 10

Differentiates group B streptococci from other streptococcal species
POS: enhanced hemolysis (arrow head)
NEG: no enhanced hemolysis

Group B strep (S. agalactia) (+)
Vs.
Other Strep (-)

Small % of Group A will come up positive

Question 11

Motility (Listeria)

Answer 11

Wet mount preparation looking for end-over-end tumbling of bacteria
Tube observation of umbrella shape (semi solid media)

Listeria (+)
 Other Bacteria (-)

Question 12

Clue Cells

Answer 12

Wet mount preparation looking for “clue cells” (stippled epithelial cells)

Gardnerella (+)
 Other bacteria (-)

Question 13

Novobiocin

Answer 13

Antibiotic susceptibility test
POS: zone > 16mm
NEG: zone < 12mm

S. saprophyticus (+)
Vs.
Other staph (-)

Question 14

PYR

Answer 14

Identification of group A strep and enterocci by prescence of L-pyrrolidonyl arylamidase
POS: bright red color
NEG: no color or orange

Group A Strep (S. pyogenes) (+)
Enterococci (+)
Vs
Other organisms (-)