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Infectous Disease > Staphylococcus > Flashcards

Staphylococcus Flashcards

1
Q

Staph Identification

A

Gram + Cocci (Purple) + Catalase Positive +Form grapelike clusters

  • S. Aureus is coagulase positive
  • purulent
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2
Q

Staph Strains

A
  • S Aureas is Coagulase Positive

- S Epidermididis and others are Coag (-) “CoNS”

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3
Q

Structural Virulence Factors

A
  • Protein A: Binds Fc portion of IgG, prevents phagocytosis, complement activation, also camoflauges
  • Polysaccharide Capsule: Impedes phagocytosis
  • Biofilm: Protein and sugar rich secretion that protects “arrested” bacteria. Mostly in CoNS
  • MSCRAMM’s- Adhesion molecules, assist in adherence to heart valves (endocarditis)
  • Teichoic Acid-Adhesion to collagen and induces cytokine release.
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4
Q

Secreted Virulence Factors

A
  • Coagulase: Fibrin clot protects and walls off abcess
  • Catalse: H2O2 -> H20 + O2. Prevents phagocyte killing
  • Leukocidins: Kill leukocytes, PVL is common one that is present in staph induced necrotizing pneumonia
  • Hyaluronidase: Allows for nutrient extraction and spreading
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5
Q

Toxins

A
  • A number of cytotoxins cause cellular damage and death
  • Exfoliative toxin
  • Toxic Shock Syndrome Toxin 1
  • Enterotoxins
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6
Q

Scalded Skin Syndrome (Ritters)

A
  • Caused by exfoliative toxin that acts on stratum granulosum. There are no cells present in blisters, just toxin.
  • Considerably more deadly in adult
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7
Q

TSST1

A
  • Toxic Shock Syndrome: is a superantigen that crosslinks T cells and activates a large number leading to:
    1. Fever
    2. Decreased BP
    3. Desquamating Rash
  • For diagnosis rule out possible other agents and see involvment of multiple organ systems
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8
Q

TSS Treatment

A
  1. Manage BP with fluids and pressors
  2. Remove source of infection, often in tampons or nasal packing, or surgically
  3. Treat with antibiotics
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9
Q

Emperical Treatment for TSS

A
  1. Clyndamicin : Protein inhibitor
  2. Vancomycin : Cell wall synthesis inhibitor (Gram +) (Be carfeul of Nephro and Ototoxicity)
  3. Carbapeneam or piperacilin/tazobactam (broad spectrum inhibitors of cell wall sythesis)
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10
Q

Specific Treatment

A
  1. MSSA: Nafcilin
  2. MSRA: Vancomycin or Linezolid
  3. Group A Strep/Clostridium Sordelli: Pen G
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11
Q

Food Poisining

A

Preformed heat stable enterotoxins. Treatment is conservative with few antibiotics and usually self limiting in 24hrs

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12
Q

HA resistance

A
  • Came first, resistance cassette is MecA which carries resistance to a number of antibiotics
  • Structural aleration in PBP2a
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13
Q

CA Resistance

A
  • USA 300 is predominant strain and is now more common in both Community and Hospital than HA
  • SCCmecIV is resistance cassete which carries fewer resistance genes
  • Resistant strains take longer and are harder to kill, but not necessarily have worse outcome (death)
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14
Q

Causes of TSS

A
  1. S Aureus, CoNS
  2. Streptococcus Pyogenes (group A Strep)
  3. Clostridium sordelli
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15
Q

Skin and Soft Tissue Infections (SSTI)

A
  • Common, S Aureus is part of flora in 10-40% of people

- Furuncles/carbuncles, cellulitis, folliculitis

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16
Q

Blood Stream Infection Diagnosis

A
  1. Fever
  2. Positive Blood Cultures
  3. Decreased BP
17
Q

Impatigo

A
  • Infection of the epidermis

- Can be caused by Staph, MSSA/MSRA or group A strep

18
Q

Blood Stream Infection Causes

A
  • Can be caused by entry from other site

- Common to see CoNS entering from catheters and other prosthetic devices

19
Q

BSI Complications

A
  • Endocarditis is largest complication, can cause damage to valves and also septic emboli that can cause stroke, infarction, or PE.
  • MSCRAMM’s help staph adhere to heart valves
20
Q

BSI TTx

A

1.Start Antibiotics
2 Remove Source of infection
3. Transesophageal Echocardiogram

21
Q

Lung Infections

A
  • Staph is less common than strep, but possible
  • Necrotizing Pneumonia with Empyema when Staph is present.
  • PVL is major virulence factor in Necrotizing Pneumonia
22
Q

CoNS Infections

A
  • Very easy to get contaminated, many CoNS are commensals
  • Easily enter and adhere to catheters or Prosthetic devices.
  • If positive test result be suspicious of false positive, but more assurance if there is catheter or prosthesis
23
Q

Staphylococcus Summary

A
  1. Gram + cocci that form cluster, Catalase (+) Coagulase (+/-)
  2. S. Aureus is more virulent than other forms
  3. Resistance is built to nafcilin and penecilin, use vancomycin instead
  4. Toxins: Exfoliative, TSST-1, Enterotoxins
  5. Endocarditis is most serious and common side effect of BSI with Staph
  6. CoNS form biofilms and can easily infect catheters or prosthetic devices

Infectous Disease (14 decks)

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