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Flashcards in L35 Deck (28):
1

What is the microscopic morphology of staph?

GP - thick peptidoglycan layer
Cocci in clusters (grapes)

2

Is SA catalase positive or negative?

Positive

3

Is SA coagulase positive or negative?

Positive

4

Does SA have a polysaccharide capsule or slime layer?

Both
Capsule - protection from phagocytosis
Slime - adherence

5

What color is SA on blood agar?

Yellow/gold

6

What are the 6 virulence factors for SA?

1. Capsule
2. Protein A
3. MSCRAMM surface adhesion proteins
4. Enzymes for tissue destruction
5. Toxin mediated tissue destruction
6. Penicillinase/antibiotic resistance

7

What is protein A?

Cell wall protein that binds IgG @ Fc so the Abs can't mark the bug for phagocytosis
Also binds VWB factor to help with platelet adhesion for increased virulence

8

What are some examples of enzymes SA uses for virulence?

Coagulase - microthrombus formation
Catalase - inactivates Hperoxide (killing mechanism)
Lipases & nucleases that hydrolyze lipids & DNA

9

How do the cytotoxins SA produces help its survival?

Cytotoxins are always produced (vs cytolytic peptides = sometimes)
Lyse cell membranes to destroy immune cells

10

What toxin does SA produce yielding scalded skin syndrome?

Exfoliative toxins

11

What toxin does SA produce yielding food poisoning?

Enterotoxin

12

What toxin does SA produce yielding shock?

Toxic shock syndrome toxin 1

13

What are the mechanisms by which SA is drug resistant?

1. Penicillinase vs beta lactams
2. mecA --> PBP2a --> methicillin & semi-synthetic penicillins (nafcillin & dicloxacillin) resistance

14

How can SA become VISA?

= vanco resistance
Acquired from VRE (vanA to alter binding site)
See thickened cell wall that vanco gets stuck in

15

Is SA colonization common?

30% population
Nose

16

What skin/ST infections might present due to SA?

Pyogenic infections:
- Impetigo
- Folliculitis
- Furuncle (boils)
- Carbuncles
- Wounds post surgery

17

What metastatic infections may present due to SA?

BACTEREMIA!!!
Pneumonia
Osteomyelitis
Septic arthritis
Endocarditis

18

What are the main virulence factors for coag negative staph?

Slime layer
Enzymes like SA
- But no toxins!

19

What coag-neg staph typically infects prosthetic material?

S. epidermidis

20

Which coag-neg staph causes UTIs?

S. saprophyticus

21

Which coag-neg staph causes native valve endocarditis?

S. lugdenensis

22

How do you diagnose SA?

Culture
- See in blood = BAD, always assume it is real & treat it
- Skin site only if near/at the site of infection (will be negative if the infection source is not there)

23

How do you diagnose coag-neg staph?

Blood culture
- Could be false positive b/c went through the skin where colonies are normally high to take sample
- Need multiple positive samples to get conclusive diagnosis this way
Direct sample from prosthetic

24

Quickly, you need to start treating a patient for staph infection before the cultures come back. What do you assume about the staph?

Assume penicillin & methicillin resistant

25

You're starting initial antibiotics for staph infection. If the patient is obviously sick - what are you choosing?

VANCO
Could go with dapto BUT not if the presentation is pneumonia
2nd choices: linezolid, ceftraroline

26

You're starting initial antibiotics for staph infection BUT patient isn't super sick. Aka you can send them home with something PO. So what are you picking?

Clindamycin
TMP/SMX
Doxycycline
MRSA
Linezolid

27

Cultures are back. The infection is serious & SUSCEPTIBLE. Which antibiotic are you going with?

Anti-staph penicillins:
- Nafcillin
- Cefazolin
2nd choice if resistant/allergic:
- Vanco
- Dapto (if not pneumo)

28

What is your choice for outpatient management of staph?

1st = penicillins
- Dicloxacillin
- Cephalexin
2nd = resistant or allergic
- Clindamycin
- TMP/SMX - but may not cover strep
- Doxycyline for CA MRSA