Bacterial Skin (lec 22) Flashcards by Wendy Pitts

Routes of infection?

1) Exogenous (disrupt skin barrier)
2) Endogenous (seeded into tissue by blood/lymph)
3) Toxin Induced (made at distant site, cause pathogenesis at/near skin)

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Abscess-Forming infections? (3)

Acne
Folliculitis
Furuncles/Carbuncles

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Acne Vulgaris etiology?

Propionibacterium acnes

G+
Anaerobe
Non-motile

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Factors contributing to Acne? (4)

1) Genetics
2) Follicular epidermal hyperproliferation from androgens
3) Excess sebum prdxn
4) P. acnes prdxn of lipase causes inflammation

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Noninflamm Acne Vulgaris caused by?

Formation of Microcomedo:

partial obstruction of follicle by sebum, keratinocytes, hair

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Noninflam Acne Vulg presents as? (2)

1) Closed comedones (whiteheads)

2) Open comedones (blackheads)

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Inflamm Acne Vulgaris caused by?

Rupture of follicular content into dermis

Nodular is most severe

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Folliculitis is?

Superficial: small papules/pustules on erythematous base, pierced by central hair

Deep: erythematous nodules

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Superficial Folliculitis caused by?

S. aureus

P. aeruginosa

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S aureus presents as what forms of folliculitis?

Impetigo of Bockhart (bearded area)

Sty (eyelid)

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P. aeruginosa presents as what form of folliculitis?

Hot tub/wetsuit
from contaminated H2O
breakout in swimsuit areas

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Furuncles are?

Boils/large folliculitis abscess
Extend thru dermis/subQ
Face/neck, thighs/butt

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Carbuncles are?

Inflamm of many hair follicles
Into dermis/subQ
Neck, back, thighs

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Spreading Soft Tissue infections include?

Impetigo

Cellulitis

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Nonbullous Impetigo caused by?

a/w?

S. aureus
S. pyogenes (GAS)

a/w acute glomerulonephritis

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Impetigo Pyoderma caused by?

Epidemiology?

strep strains

1-5 yo
warm/moist weather

Pyoderma infection characteristics?

Intradermal vesicles
Honey crusting
Contagious vesicles

Bullous Impetigo caused by?

S. aureus exfoliatin toxin

digests epiderm

Bullous Impetigo presentation?

Large, superficial, thin-walled blisters

Crust when burst
Contagious bullae (microbe and toxin in blister, not systemic)

Cellulitis is?

caused by?

subQ CT infection from toxins/inflamm response

S. aureus/S. pyogenes

(P) G- acinetobacter (trauma), pasturella (cat/dog), aeromonas (fresh H2O), vibrio (salt H2O)

Cellulitis presentation?

Break in infected skin -> seeding

Acute inflamm subQ CT into lower dermis
Few microbes

Heat, Erythema, Edema, Tenderness (HEET),
“sunburn” diffuse borders

Cellulitis labs when?

What tests?

Only if:
immunocompromised, skin lesions, large area, spreading

Cx
Imaging to r/o necrotizing fasciitis

Cellulitis tx?

elevation
ABX
No NSAIDS (mask indicators, ↓ immune response)

Necrotizing Fasciitis caused by?

Type 1: > 1 faculative aerobe and anaerobe

Type 2: Flesh-eating Group A strep pyogenes

Necrotizing Fasciitis Type 1 risk factors?

↓ immune, DM, surgery

Necrotizing Fasciitis Type 2 risk factors?

Anyone

Necrotizing Fasciitis infection route?

deeper tissues -> subQ, muscle fascia ``` spreads along mm fascia (poor bloody supply) mm spared (good blood supply) ```

Necrotizing Fasciitis presentation?

Acute onset HEET, shiny ↑↑ pain ↑↑ progression red/purple -> cutaneous anesthesia (dead bv/nn) -> blue/gray FAILURE TO RESPOND TO ABX (poor blood source = poor delivery)

Necrotizing Fasciitis advanced infection presentation?

fever, tachy, toxicity (confused) | putrid if type 1 anaerobe

Necrotizing Fasciitis presentation w/ surgery?

swollen/gray fascia, thin, brown exudate extensive undermining, tissue separates along fascial planes

Necrotizing Fasciitis diagnostics?

Surgical Gram stain/Cx/Rapid strep MRI (extent of inf)

Necrotizing Fasciitis tx?

debridement ABX HB O2 (kills anaerobes) Maggots

Myonecrosis/Gas gangrene caused by?

C. perfringens A G variable in wound Spores Anaerobe

C. perfringens virulence factor? Route of infection?

α toxin phospholipase C (cytolytic) Reduced O2 tension (trauma/microbes) -> Anaerobic cells/spores produce exotoxin/H2 gas

Myonecrosis presentation?

EMERGENCY Rapid onset of pain Skin pale -> bronze -> edema -> bullae Exudate smells sweet (foul = Ø c. perf) Fever, tachy, confusion

Myonecrosis diagnostics?

Bx | Stain = mm necrosis, variable G, Ø PMN

Myonecrosis tx?

debridement HBO2 ABX