Lab Tests Gram Positive Cocci

Question 1

SBA

Answer 1

Enriched differential: has red blood cells
Differentiates hemolysis

Question 2

Alpha Hemolysis

Answer 2

Partial hemolysis of red blood cells, greenish color around colonies because of oxidation of hemoglobin

Question 3

Beta Hemolysis

Answer 3

Full hemolysis of red blood cells

Question 4

Gamma Hemolysis

Answer 4

No hemolysis of red blood cells

Question 5

Chocolate Agar

Answer 5

Only enriched
Blood cells are lysed for easy access so the organisms grow even better

Question 6

Mannitol Salt Agar

Answer 6

Selective differential
Salt = selects for Staph, inhibits Strep
Mannitol: differential, red to yellow pH change if can utilize mannitol

Question 7

Catalase Reagent

Answer 7

Hydrogen peroxide
Organisms that have catalase can break down H2O2 into water and O2, O2 causes the gas bubbles
Differentiates: staph +, strep -

Question 8

Bacitracin Test Method

Answer 8

Antibiotic resistance
Differentiates +: micro (s), staph ep (r)
Differentiates -: , strep agal (r), strep pyo (s)

Question 9

Coagulase Test Method

Answer 9

Clumping factor (slide): bound to cell walls, acts directly on fibrinogen
Extracellular coagulase (tube): liberated by the cells
Differentiate: staph aur +, staph epi -

Tube test needed for confirmation of S. aur after + slide test bc some biotypes of S. aur ONLY have extracellular

Question 10

Novobiocin Test Method

Answer 10

Antibiotic
Differentiate: staph epi (s), staph sapro (r)

Question 11

Bile Esculin Test Method

Answer 11

Selective differential
Sodium azide and oxgall: selective against G- and most G+
Esculin: differential, hydrolize esculin in presence of bile
Turns black when hydrolized and combined with ferric citrate

Differentiate: strep pneumo -, viridans -, entero +

Question 12

Bile Solubility Test Method

Answer 12

Bile salts or bile lyses colonies due to intracellular autolytic enzymes
Differentiate: *strep pneumo *+, viridans -, enter -

Question 13

CAMP Test Method

Answer 13

CAMP factor acts with beta-lysin of staph aur to produce enhanced lysis of RBCs, clear arrowhead zone if positive
Differentiate: strep agal +, strep pyo -

Question 14

Optochin Disc Test Method

Answer 14

Antibiotic
Differentiate: strep pneumo (s), viridans (r), entero (r)

Question 15

PYR Test Method

Answer 15

PYRase in organism catalyzes hydrolysis of PYR, interacts with color indicator and turns red
Differentiate: strep agal -, strep pyo +, entero +

Question 16

Micrococcus luteus

Answer 16

Gamma
Catalase +
Bacitracin (s)

Question 17

Staphylococcus aureus

Answer 17

Beta (the ONLY catalse + beta)
Catalse +
Coagulase tube +
Mannitol salt agar +, utilizes

Question 18

Staphylococcus epidermidis

Answer 18

Gamma
Catalse +
Bacitracin (r)
Coagulase tube -
Novobiocin (s)
Mannitol -

Question 19

Staphylococcus saprophyticus

Answer 19

Gamma
Catalse +
Novobiocin (r)
Mannitol -

Question 20

Streptococcus agalactiae

Answer 20

Small beta
Catalase -
Bacitracin (r)
PYR -
CAMP +

Question 21

Streptococcus pyogenes

Answer 21

Heavy beta
Catalse -
Bacitracin (s)
PYR +
CAMP -

Question 22

Streptococcus pneumoniae

Answer 22

Alpha
Catalase -
Bile esculin -
Bile solubility +
Optochin (s)

Question 22

Viridans streptococcus

Answer 22

Alpha
Catalse -
Bile esculin -
Bile solubility -
Optochin (r)

Question 22

Enterococcus faecalis

Answer 22

Gamma
Catalse -
PYR +
Bile esculin +
Bile solubility -
Optochin (r)