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Unit 1 ID+LC > Staphylococci > Flashcards

Staphylococci Flashcards

1
Q

1 cause of bacteremia

A

Staph

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2
Q

Staph grows in pairs, groups or chains?

A

Pairs + Groups

- strep is chains

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3
Q

Staph toxin actions:
Enterotoxin A-1
Exfoliatin A-B
TSST-1

A

Enterotoxin A-1
- vagal stimulator

Exfoliatin A-B
- Granular cell layer cleavage

TSST-1
- TNF, IL-1 stimulator

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4
Q

Exotoxins vs Endotoxins (123)

A

Exotoxins source:
secreted from certain Gram +/- species
- Polypeptide

Endotoxins source:
outer cm of most Gram -
(not secreted)
- Lipopolysaccaride (released when lysed)

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5
Q

How to identify Staphylococci? (start with GPC ID)

A
  1. GPC aerobic
  2. Blood +, Chocolate +, MacConkey -
  3. Catalase Positive

*MacConkey suppress gram + growth

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6
Q

S. aureus is coagulase _____ (+/-?)

A

coagulase positive
- golden

(staphylococci 31+ species are coag - and white)

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7
Q

how is S. aureus clumping factor positive?

A

due to its cell wall protein
- similar binding proteins to fibronectin and collagen

It binds to fibrinogen and converts it to fibrin causing clumping and protection from phagocytosis (very virulent to hu)

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8
Q

Significance of S. aureus being Protein A positive?

A

S. aureus produces Protein A

Protein A binds to Fc receptor of IgG, which prevents antibody mediated phagocytosis
(nl foreign bact bind at FAV site –> phago)

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9
Q

lipotechoic acid - adhesin

A

Staph techoic acids bind to epithelial cells via cell attachment to fibronectin

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10
Q

2 types of cytolytic proteins that staph contains that cause tissue damage.

A
  1. Hemolysins (a, b, gamma)
    - Red cell lysis
    - tissue damage
  2. Panton-Valentine Leucocidin
    - white cell lysis
    - protection from phagocytosis
    - invasive skin disease
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11
Q

Exfoliatin A + B effects

A

two immunologically distinct toxins with identical effects
- bind to GM4 glycolipids (infants)

Causes separation at granular-cell layer (desmosomes)

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12
Q

Enterotoxins of s. aureus

A

heat and acid stable proteins
8 serotypes
30-40% of s. aureus strains

preformed toxin in contaminated food causes vomiting and diarrhea when ingested

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13
Q

Most common cause of food poisoning

A

Enterotoxins due to s. aureus

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14
Q

TSST-1 toxin mediated disease

A

toxic shock syndrome

Exposure to TSST-1 S. aureus strain –>
growth of organism that promote toxin production –>
No pre-existing antibody to toxins –>
superantigen stimulates cytokines –> causes endothelial leakage

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15
Q

Where are they found in nl flora?

  1. S. aureus
  2. Coag neg staph
A
  1. S. aureus
    - nose, throat, vagina
  2. Coag neg staph
    - skin, throat
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16
Q

MRSA

A

carry mecA gene
Codes for altered PBP: PB2A
- decreases beta lactam binding and cell wall inhibition

17
Q

Vancomycine intermediate s. aureus (VISA) and VRSA (vanco resistance)

A

Vancomycin inhibits D-ala D-ala cross polymerization in peptidoglycan layer

VISA have increase # peptidoglycan layer

VRSA have vanA gene from enterococcus

18
Q

Alternatives you can use if bug is VISA or VRSA

A

trimethoprim/sulfa
linezolid
Synercid
daptomycin

19
Q

D test

A

erythromycin-induced clindamycine resistance in Clindamycin-susceptible, Erythromycin-resistant S. aureus

S. aureus can harbor inducible erm methylase system or macrolide efflux pump system.
- First one can cause resistance to clindamycin due to mutation and constitutive expression of erm. Need to differentiate –> use D test.

  • be wary of using clindamycin or macrolides bc of mutation occurs
20
Q

Which is a localizing presentation, staph or strep?

A

Staph = localizing disease

ie: furuncles/boils, lymphadenitis

21
Q

How can staph cause bacteremia?

A
  1. Respiratory colonization –> otitis, sinusitis pneumonia –> bacteremia
  2. Cutaneous injury/defect –> cellulitis/boils –> bacteremia

bacteremia can result in either disseminated septicemia or deep focal infection (osteomyelitis, arthritis, pericarditis, endocarditis)

22
Q

Osteomyelitis

A

hematogenous spread
local bone absecess

staph most common cause

23
Q

Most common cause of osteomyelitis

A

staph

24
Q

Sinusitis

A

staph is uncommon cause of local respiratory spread:

- otitis, sinusitis, pneumonia (CF)

25
Q

Disseminated staph septicemia does not localized, but what is it often associated with?

A

endocarditis or thrombophlebitis

Protease + strains

26
Q

Phagocytosis is the major host defense, how does staph impede this?

A
  1. protein A
  2. Panton-valentine leukocidin
  3. Localizing factors (clumping factor, coagulase)
27
Q

Chronic granulomatous disease

A

Sex linked recessive neutrophil defect

Most common neutrophil defect

Impaired H2O2 mediated intracellular killing

28
Q

Job’s syndrome (214)

A

Hyper IgE

Cold (noninflammed) staph abscess

Poor neutrophil chemotaxis to site of infxn

29
Q

Do you see strawberry tongue in staph scarlet fever?

A

no

*scarlet fever is caused by exfoliatin
seen in strep scarlet fever

30
Q

Toxic shock syndrome

  • Virulence factor
  • signs
A

TSST-1
Enterotoxins

  1. Acute fever
  2. Erythroderma (desquamation usually late)
  3. Hypotension
  4. Multi-organ system involvement
31
Q

Scalded skin

  • Virulence factor
  • Clinical findings
A

Exfoliatins

  1. Painful Erythroderma
    • Nikolsly sign
  3. Bullous Impetigo
32
Q

Which staph virulence factors causes vomiting and diarrhea?

A

Preformed Enterotoxins (in food)

  • it is heat stable and is not destroyed by cooking
  • an exotoxin (not endotoxin)
33
Q

Exfolatins from S. aureus can cause what?

A

Scalded skin syndrome

Staphylococcal scarlet fever
diff from strep

34
Q

Tx for S. aureus
Tx for MRSA
Tx for Coag - Staph

A

S. aureus:

  1. Methicillin
  2. Cephalosporins
  3. Vancomycin

MRSA:

  1. Vancomycin
  2. Bactrim

Coag - Staph

  1. Vancomycin
  2. Rifamin (alwaysuse with primary drug)
35
Q

Tx regimens

A
  1. Draining critical for focal infxn
  2. Antibiotic duration
    - Mild infxn: 7-10 days
    - Severe infxn: 3-6 weeks
  3. Add clindamycin in TSS to shut off toxin production

Unit 1 ID+LC (32 decks)

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