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Skin > Agents of Bacterial Skin Infections: Streptococci > Flashcards

Agents of Bacterial Skin Infections: Streptococci Flashcards

1
Q

Origins of Skin & Soft Tissue Damage

A
  • Exogenous: Direct invasion of microbes from external environment
  • Endogenous: Invasion of microbe from internal source, such as blood or organ
  • Toxin Mediated: manifestations from an infection at a distant site
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2
Q

Categories of Skin Flora

A
  • Resident: Mostly bacteria & include Staphylococcus epidermidis and Prpionibacterium acnes
  • Transient: frequently Staphylococcus aureus and Streptococcus pyogenes, but can be other bacteria, fungi, & viruses
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3
Q

Response of Skin to Invading Infection

A
  • Spreading Infection:
    • Impetigo: Confined to epidermis
    • Erysipelas: Involved dermal lymphatics
    • Cellulitis: subcutaneous fat layer
  • Abcess formation:
    • Folliculitis
    • Boils (Furnuncles)
    • Carbuncles
  • Necrotizing Infections:
    • Fasciitis
    • Gas gangrene (myonecrosis)
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4
Q

Streptococci in General

A
  • Pyogentic: invasive, pus forming, obligate extracellular, w/ anti-phagocytic factors
  • Gram positive cocci
  • Catalase negative (doesn’t convert H2O2)
  • Grouped based on hemolytic pattern:
    • Beta: clearing due to hemolysins
    • Alpha: green due to partial clearing
    • Gamma: no clearing
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5
Q

Group A Streptococci

A
  • Streptococcus Pyogenes
  • Rapid test for group A
  • Chains
  • beta hemolytic, catalase negative
  • sensitive to bacitracin
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6
Q

Streptococci Pyogenes Virulence Factor:

M Proteins

A
  • M protein: binds bacteria to epidermis
    • Anti-phagocytic help bind and colonize
    • Molecular mimicry: cross reacts w/ mammalian epitopes
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7
Q

Streptococci Pyogenes Virulence Factor:

Hyaluronic acid Capsule

A
  • capsule: identical to normal tissue
  • anti-phagocytic
  • Antibody to capsule not protective
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8
Q

Streptococci Pyogenes Virulence Factor:

Pyrogenic exotoxins

A
  • superantigens stimulate production of cytokines

* Scarlet fever and TSS like syndrome

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9
Q

Streptococci Pyogenes Virulence Factor:

Streptolysin O

A

-hemolytic and toxic to cell
-O2 Labile
-Antigenic
Antibody to this is basis of anti-streptolysin O test

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10
Q

Streptococci Pyogenes Virulence Factor:

DNAases

A

-Depolymerizes cell free DNA in purulent lesions

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11
Q

Streptococci Pyogenes Virulence Factor:

Streptokinase

A
  • Lyses blood clots

- Helps bacteria spread

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12
Q

Streptococci Pyogenes Virulence Factor: C5a peptidase

A

-degrades complement component that attracts PMNs

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13
Q

Pharyngitis: w/ Scarlet Fever

A
  • Normal pharyngitis has inflammation of the oropharynx
    • Petechia on soft palate
  • Scarlet Fever
    • Fiery red tongue with prominent papillae (raspberry tongue); white-coated tongue through which hyperemic papillae project (strawberry tongue)
    • Circumoral palor
    • desqumation following red rash
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14
Q

Impetigo

A
  • Begins as a red sore near the nose or mouth
  • breaks, leaking pus or fluid, and forms a honey-colored scab
  • Lymph nodes in the affected area may be swollen, but fever is rare
  • Climate and Hygiene affect incidence
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15
Q

Erysipelas

A
  • rythematous skin lesion enlarges rapidly and has a sharply demarcated raised edge
  • red, swollen, warm, hardened and painful rash, similar in consistency to an orange peel.
  • high fevers, shaking, chills, fatigue, headaches, vomiting,
  • Affects lymphatics
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16
Q

Cellulitis

A
  • area which is red, hot, and tender
  • Skin redness or inflammation that gets bigger as the infection spreads
  • Affects subcutaneous fat layer
  • Tight, glossy, “stretched” appearance of the skin
  • Hair loss at site of infection
17
Q

Necrotizing fasciitis

A
  • Infection of deeper subcutaneous tissue and fasciae
  • Spreads rapidly in deep tissue
  • Rapid demise
18
Q

Streptococcal Toxic Shock Syndrome

A
  • fever, erythroderma, rapid-onset hypotension, & multisystem organ involvement
  • superantigen toxin allows nonspecific binding of MHC II with T cell receptors, resulting in T cell activation
  • Patients are Bacteremic: infection enters blood stream
19
Q

Rheumatic Fever

A
  • Occurs in 6-15 y/o
  • Following throat infection w/ rheumatogenic M types of GAS
  • Cross reaction b/t M-antibodies and heart tissue
20
Q

Acute Glomerulonephritis

A
  • Following throat or skin infection w/ nephritogenic M types
  • Renal injury due to deposition of antigen-antibody complexes in glomeruli
21
Q

PANDAS

A

Pediatric Autoimmune Neuropsychiatric Disorder Assoociated w/ group A Streptocci

  • OCD or tic
  • pediatric abrupt onset
  • Associated w/ GAS infection
  • Motoric hyperactivity, choreiform movements, or tics

Skin (6 decks)

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