Bugs - Staph

Question 1

how is staphylococci differentiated from streptococci and enterococci?

Answer 1

microscopic morphology catalase +

Question 2

s. aureus virulence factors

Answer 2

capsule(sticky)

Protein A: binds IgGs, inhibits phagocytosis

MSCRAMM: adhesion proteins

enzymes

toxins

Question 3

what are the virulent enzymes in s. aureus related to tissue destruction?

Answer 3

coagulase, hyaluronidase, catalase, fibrinolysin, lipases, nucleases

Question 4

what are the constitutive s. aureus toxins?

Answer 4

hemolysins - destroy erythrocytes

leukocidin - destroys leukocytes and macrophages

cytolytic peptides - recruit PMN then kill em(overproduced in CA-MRSA)

Question 5

describe the non-constitutive toxins of s. aureus and their associated syndromes

Answer 5

exfoliative toxin –>scalded skin syndrome

enterotoxin(premade) –> food poisoning

toxic shock syndrome toxin –> sepsis

Question 6

what causes methicillin resistance?

Answer 6

acquiring mecA –> PBP2a b-lactams cant bind their target enzyme(transpeptidase)

Question 7

what two resistances prevent vancomycin use?

Answer 7

VISA(vanco intermediat s. aureus) –> thickened wall

VRE(vanco resistant entero) –> changes d-ala binding to

Question 8

pyogenic cutaneous disease caused by s. aureus

Answer 8

impetigo, folliculitis, furuncles, carbuncles, wound infection

Question 9

pyogenic systemic disease caused by s. aureus

Answer 9

pneumonia

empyema

osteomyelitis

septic arthritis

endocarditis

bacteremia

Question 10

newborn pt presents with erythematous skin with desquamation and widespread fluid filled, thin walled blistering. Culture from blister sample is negative for any bacteria. What toxin-related disease is on the differential?

Answer 10

scalded skin syndrome via exfoliative toxin from s. aureus

Question 11

what is a localized SSSS

Answer 11

staphylocococcus scalded skin syndrome when localized, it is called bullous impetigo; blisters are filled with bacteria and inflammatory cells; local spread from infected wound

Question 12

pt presents with acute onset diarrhea, NV, and abdominal pain. pt has no fever. later, a bacterial culture returns with s. aureus bacteria found in stool. what was the cause of this disease?

Answer 12

the CAUSE is the pre-formed enterotoxin created by s. aureus it is both heat stable AND a superantigen, inducing peristalsis and inflammation(NVD)

Question 13

36 y/o female pt presents with an acute onset erythematous rash with desquamation. Pt has a fever and hypotension. what s. aureus toxin causes these symptoms??

Answer 13

TSST-1 is most common causes toxic shock syndrome

Question 14

name the virulence factors of coagulase negative staphylococci

Answer 14

slime layer(biofilm)

many same enzymes as s. aureus

NO TOXINS

antimicrobial resistance common

Question 15

name the most common pathological route of infection for:

s. epidermidis

s. saprophyticus

s. lugdenensis

Answer 15

s. epidermis(and others) commonly adhere to prosthetic joints, valves, and shunts

s. saprophyticus commonly causes UTIs

s. lugdenensis commonly causes native valve endocarditis

Question 16

describe empiric therapy for staphylococcal infections

what are good empiric outpatient therapies?

Answer 16

if pt. is sick(bacteremia/pneumonia)-

• vancomyicn
• daptomycin
• linezolid
• ceftaroline

if pt. is not “sick”(outpatient skin/soft tissue) -

• clindamycin
• TMP/SMX
• doxycycline
• linezolid

Question 17

first line agents against MSSA bacteremia

Answer 17

nafcillin, cefazolin(dont need vanco, dapt if not MRSA)