Staphylococci

Question 1

What are the major causes of a UTI?

ƒ

Answer 1

E. coli (most common)
Staphylococcus saprophyticus (seen in sexually active young women)
Klebsiella
Proteus mirabilis (urine has ammonia scent)- struvite stones
Serratia marcescens

Question 2

What are the 3 major pathogenic species of staphylococccus?

Answer 2

Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus

Question 3

What staph species are coagulase +? What staph species are coagulase -?

Answer 3

+: S. aureus

-: S. epidermidis, S. saprophyticus

Question 4

Why is it important to differentiate staph from strep?

Answer 4

Most staph are penicillin resistant

Question 5

Which species of Staph is novobiocin sensitive? What species of Staph is novobiocin insensitive?

Answer 5

Sensitive: S. epidermidis
Insensitive: S. saprophyticus

Question 6

Staph aureus is beta hemolytic, however, Staph aureus can be differentiated from other beta hemolytic cocci based on what blood agar finding?

Answer 6

Staph elaborates a golden pigment on blood agar

Question 7

What is the action of coagulase?

Answer 7

Activates prothrombin to form clots

Question 8

What proteins are made by S. aureus to protect the organism by inhibiting the immune response?

Answer 8

Protein A- binds IgG, inhibiting phagocytosis/opsonization

Coagulase- forms protective fibrin barrier

Question 9

What exotoxins are made by S. aureus that mediate disease in the host?

Answer 9

Exfoliatin- scalded skin syndrome
Enterotoxin- food poisoning
Toxic shock syndrome toxin (TSST-1)

Question 10

How does TSST-1 cause toxic shock syndrome?

Answer 10

Superantigen that binds to MHCII molecules on antigen presenting cells; MHCII-TSST complex causes massive T cell response

Question 11

How would you expect a patient to present with TSS mediated by S. aureus?

Answer 11

Fever
Rash
Shock
Organ failure
Desquamation

Question 12

Contrast the associated causes of S. aureus TSS with S. pyogenes TSS.

Answer 12

S. aureus- associated with prolonged use of tampons or nasal packing
S. pyogenes- associated with skin infection

Question 13

What diseases result from direct organ invasion by S. aureus?

Answer 13

Pneumonia
Meningitis
Osteomyelitis
Acute bacterial endocarditis
Septic arthritis
Skin infections
Bacteremia/sepsis
UTI

Question 14

S. aureus is a rare but severe cause of CAP. It usually follows a viral influenza upper respiratory illness with rapid destruction of the lung parenchyma What findings might you see on CXR?

Answer 14

Cavitations
Pleural effusion
Empyema

Question 15

What is the most common cause of acute bacterial endocarditis?

Answer 15

S. aureus

Question 16

What are possible complications due to S. aureus that can arise in a patient with a catheter?

Answer 16

Bacteremia/sepsis
Septic shock
Endocarditis

Question 17

What protein mediates MRSA resistance?

Answer 17

Penicillin binding protein 2A

Question 18

How does vanA mediate vancomycin resistance in VRSA?

Answer 18

Encodes proteins that modify the D-alanine-D- alanine terminus of the cell wall to D-alanine-D-lactate which has a low affinity for vancomycin

Question 19

S. epidermidis is known for infecting prosthetic devices and IV catheters as well as contaminating blood cultures. How does it infect prosthetic devices?

Answer 19

Capsule

Biofilm

Question 20

Is S. epidermidis coagulase positive or negative?

Answer 20

Negative

Question 21

Is S. saprophyticus coagulase positive or negative?

Answer 21

Negative

Question 22

Is S. aureus coagulase positive or negative?

Answer 22

Positive

Question 23

Is S. epidermidis novobiocin sensitive or resistant?

Answer 23

Sensitive

Question 24

Is S. saprophyticus novobiocin sensitive or resistant?

Answer 24

Resistant

Question 25

What is the second most common cause of uncomplicated UTI in young women?

Answer 25

S. saprophyticus