L35 Flashcards
What is the microscopic morphology of staph?
GP - thick peptidoglycan layer
Cocci in clusters (grapes)
Is SA catalase positive or negative?
Positive
Is SA coagulase positive or negative?
Positive
Does SA have a polysaccharide capsule or slime layer?
Both
Capsule - protection from phagocytosis
Slime - adherence
What color is SA on blood agar?
Yellow/gold
What are the 6 virulence factors for SA?
- Capsule
- Protein A
- MSCRAMM surface adhesion proteins
- Enzymes for tissue destruction
- Toxin mediated tissue destruction
- Penicillinase/antibiotic resistance
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
What are some examples of enzymes SA uses for virulence?
Coagulase - microthrombus formation
Catalase - inactivates Hperoxide (killing mechanism)
Lipases & nucleases that hydrolyze lipids & DNA
How do the cytotoxins SA produces help its survival?
Cytotoxins are always produced (vs cytolytic peptides = sometimes)
Lyse cell membranes to destroy immune cells
What toxin does SA produce yielding scalded skin syndrome?
Exfoliative toxins
What toxin does SA produce yielding food poisoning?
Enterotoxin
What toxin does SA produce yielding shock?
Toxic shock syndrome toxin 1
What are the mechanisms by which SA is drug resistant?
- Penicillinase vs beta lactams
2. mecA –> PBP2a –> methicillin & semi-synthetic penicillins (nafcillin & dicloxacillin) resistance
How can SA become VISA?
= vanco resistance
Acquired from VRE (vanA to alter binding site)
See thickened cell wall that vanco gets stuck in
Is SA colonization common?
30% population
Nose
What skin/ST infections might present due to SA?
Pyogenic infections:
- Impetigo
- Folliculitis
- Furuncle (boils)
- Carbuncles
- Wounds post surgery
What metastatic infections may present due to SA?
BACTEREMIA!!! Pneumonia Osteomyelitis Septic arthritis Endocarditis
What are the main virulence factors for coag negative staph?
Slime layer
Enzymes like SA
- But no toxins!
What coag-neg staph typically infects prosthetic material?
S. epidermidis
Which coag-neg staph causes UTIs?
S. saprophyticus
Which coag-neg staph causes native valve endocarditis?
S. lugdenensis
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)
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
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
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
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
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)
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
