Micro - staphylococcus spp

Question 1

what is staph spp gram stain & morphology?

Answer 1

Gram pos cocci in clusters (“grape-like”

Question 2

what is the key biochemical test that differentiated staph vs strep spp?

Answer 2

catalase test
- staph - cat POS
- strep - cat NEG

Question 3

what 2 forms of the coagulase test exist?

Answer 3

slide coagulase = bound coagulase/clumping factor
tube coagulase = free coagulase

Question 4

describe Staph. aureus on BAP

Answer 4

round, golden yellow (butter like) colonies , beta hemolytic

Question 5

what test detects MRSA - methicillin resistant ?

Answer 5

cefoxitin disk test –> mecA gene

Question 6

what are the major virulence factors of Staph. aureus ?

Answer 6

• protein A (binds to Fc region of IgG)
• enterotoxin (food poisoning)
• TSST-1
• exfoliative toxin (scalded skin syndrome)
  etc etc

Question 7

what disease is assc w/ S. aureus entertoxin ?

Answer 7

food poisoning - heat stable toxin

Question 8

what disease is assc w/ TSST-1 from s. aureus ?

Answer 8

toxic schock syndrome

Question 9

what type of hemolysis does Staph aureus show?

Answer 9

beta hemolysis

Question 10

what organism is Novobiocin resistant?

Answer 10

staph sapRophyticus

Question 11

what organism is Novobiocin sensitive?

Answer 11

Staph. epidermis

Question 12

which staph spp is most assc w/ UTIS in young, sexually active females?

Answer 12

staph. saprophyticus

Question 13

which staph spp commonly colonizes skin & often assc w/ infections of prosthetic devices?

Answer 13

staph. epidermidis

Question 14

what virulence factor allows S. epridermidis to infect prosthetic devices ?

Answer 14

biofilm (slime layer)

Question 15

what biochem test helps differentiates staph aureus from other staph spps?

Answer 15

coagulase test
- staph. aureus = POS
- staph epi. , staph. saprophyticus = NEG

Question 16

on a MSA plate, 4 different staph spp are streaked in their own quadrant. the MLS tech observes one quadrant to have produce a bright yellow color colonies while the other colonies remained colorless. what can org can be suspected?

Answer 16

staph aureus is suspected due to the yellow color colonies produced.
** MSA is differential of staph spp organisms. coagulase POS org (staph aureus) produce yellow color vs CONStaph produce colorless pink background

Question 17

what is the gene mutation of MRSA?

Answer 17

mecA gene –> PBP2a prod –> B-lactams cannot bind

Question 18

what is typical antibiotic to treat MRSA?

Answer 18

vancomycin

Question 19

what test confirms Staph. aureus protein A presence ?

Answer 19

Latex agglutination test (detect protein A + clumping factor)

Question 20

A 27-year-old man presents with a painful, pus-filled boil on his thigh. Gram stain of the drainage shows gram-positive cocci in clusters. On blood agar, the colonies are β-hemolytic, golden-yellow, and catalase and coagulase positive.

Which toxin is MOST associated with this organism’s ability to cause abscesses?

A. TSST-1
B. Panton-Valentine leukocidin (PVL)
C. Enterotoxin A
D. Exfoliative toxin

Answer 20

B. PVL

TSST-1 –> toxic shock syn
Entertox A –> food poisn
Exfoliat. tox. –> scalded skin synd

Question 21

A 76-year-old man with a prosthetic heart valve has a fever. Two sets of blood cultures grow gram-positive cocci in clusters within 48 hours. The organism is catalase positive, coagulase negative, and novobiocin sensitive.

What is the MOST likely organism?

A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Staphylococcus saprophyticus
D. Micrococcus spp.

Answer 21

B. Staph epi.

Novobiocin key test to diff. b/w staph epi & staph. sapRophyticus
- staph sapRophyticus = Novo Resistance
- staph epi = Novo Sensi

Question 22

A nasal swab taken for pre-surgical screening grows catalase positive, coagulase positive gram-positive cocci. Cefoxitin disk diffusion shows resistance.

Which gene is responsible for this resistance?

A. vanA
B. mecA
C. ermC
D. spa

Answer 22

B. mec A –> MRSA

Question 23

A culture grows yellow colonies of Gram-positive cocci. The organism is catalase positive, forms tetrads, and is modified oxidase positive.

What is the likely organism?

A. S. aureus
B. S. epidermidis
C. Micrococcus luteus
D. S. saprophyticus

Answer 23

C. Micrococcus

tetrads key morphology

Question 24

what does coagulase test detect?

Answer 24

• enzyme that converts fibrinogen –> fibrin
• causes plasma clot formation

Question 25

what is the difference b/w slide vs tube coagulase tests?

Answer 25

- slide = detect BOUND coagulase (clumping factor) - tube = detect FREE coagulase

Question 26

what does MSA stand for? what does is select/differentiate ?

Answer 26

MSA = Mannitol Salt Agar MSA is a selective & differential media. selective for staph spp & differenties b/w 7.5% NaCl salt tolerant staph aka STAPH Aureus - S. aureus = yellow colonies

Question 27

what does CoNS stand for & why are they important?

Answer 27

CoNS = coag neg staph - norm skin flora & usually contaminants