L 69 Skin and Subcutaneous Bacterial Infections Flashcards Preview

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Flashcards in L 69 Skin and Subcutaneous Bacterial Infections Deck (38):

Some characteristics of skin that make it a good defense to disease

Acidic pH
Lower temperature than body
Low moisture
Excreted sebum, salt, urea, fatty acids
Normal microbiota: Staph. epidermis, Micrococcus luteus, E. coli
Langerhans cells in the skin to capture and present microbes to T-Cells


Name for a flat, non-palpable skin lesion



Name for palpable skin lesions



Name for palpable fluid-filled lesions



Name for palpable skin lesions filled with pus



What are the 5 factors that determine if you will get acne vulgaris?

1) Genetics
2) Follicular hyperkeratinization: increased androgen production increases proliferation of keratinocytes
3) Increased sebum production: regulated by hormones
4) Propionibacterium acnes: bacteria lives in follicles and releases pro-inflammatory mediators
5) Inflammation: Proliferation of P. acnes releases enzymes, surface proteins, heat-shock proteins


Characteristics of P. acnes

Gram (+)
Pleomorphic bacterium
Aerotolerant anaerobe
Normal skin flora, likes sebaceous glands
Can be an opportunistic infection in patients with prosthetic devices and I.V. lines


Acne Vulgaris treatment

Retinoids: comedolytic and anti-inflammatory, adapalene, tretinoin, oral isotretinoin

Antibiotics: erythromycin and clindamycin
doxycyclin and minocycline

Benzoyl peroxide: antimicrobial


Acne vs folliculitis

Acne is a type of folliculitis


What is folliculitis?

superficial infection of the hair follicles with purulent material in the epidermis


What bacteria are the cause of folliculitis?

Staph. aureus
Pseudomonas auruginosa


Characteristics of S. aureus

Gram (+) coccus
Catalase positive (distinguishes it from strep)
Normal flora on much of the skin


Enzymes of S. aureus infection

Coagulase: clots the plasma to form a fibrin protective layer around it
Hemolysis: lyses RBC's
Leukocidin: lyses WBC's to release tissue damaging enzymes that damage eukaryotic membranes=> necrotic pulmonary disease
Clumping Factor: binds fibrinogen and causes clot formation


Forms of S. aureus folliculitis

Folliculitis barbae: areas of shaving, nasal carriers of staph, erythematous follicular papules that rupture and leave a yellow crust

Sty (hordeolum): folliculitis of the eyelid


Characteristics of Pseudomonas aeruginosa

Gram (-) bacilli
Opportunistic pathogen
Fruity smell
Pyocyanin–blue pus
Pyocerdin–green fluorescent siderophore


P. auruginosa type of folliculitis

Hot Tub folliculitis
8-48 hours after infection
Itchy maculopapular rash, some pustules
Systemic comoponent: fever, headache, sore throat, malaise, GI distress
Usually self-limiting

Ecthyma gangrenosum: cutaneous infection from bacteremia


Folliculitis treatment

S. aureus: mild resolves, otherwise topical mupirocin or clindamycin, or oral dicloxacillin for MSSA; TMP/SMX, clindamycin, doxycycline for MRSA

P. aeruginosa: self-limited, resolves 7-10 days, severe cases oral ciprofloxacin


What is a furuncle?

Caused by S. aureus
Folliculitis progresses, purulent material from a single opening, in areas of friction and perspiration (face, neck, axillae, buttocks)
Pururlent material extends through dermis into sub q tissues to form abscesses


What is a carbuncle?

S. aureus caused
Aggregate of connected furuncles


Treatment of furuncles and carbuncles

Warm compress
Incision and drainage

Recurrent: Mupirocin topical applied to nares, axillae, perineum for 5 days with or without clindamycin

Treatment is to prevent hematogenous spread => endocarditis, sepsis and osteomyelitis


Pyoderma and its forms

Pyoderma: bacterial skin inflammation marked by pus-filled lesions

Impetigo (bullous and non-bullous) and ecthyma are variants

Pyoderma and impetigo limited to epidermis
Ecthyma is when it spreads down to the dermis


Nonbullous Impetigo
(impetigo contagiosa)

All ages, but mostly kids 2-6 years
S. aureus or GAS
spread by contact with the lesions, self-infection spreads it


Strep. pyogenes characteristics

Also called GAS or GABHS
Gram (+) cocci
Mostly spreading infections

Virulence factors:
-SPE–Strep Pyrogenic Exotoxins A-C, these cause rash and can lead to Scarlet fever
-M protein: fimbriae/pili associated, impede phagocytosis, creates sequelae like rheumatic fever & acute poststreptococcal glomerulonephritis


Spreading enzymes for Impetigo Contagiosa

DNase: reduces viscosity of lysed cell contents

Hyaluronidase: invasin

Streptokinase: disolves blood clots, invasin


Nonbullous inpetigo
(Impetigo contagiosum) description

Staph or Strep but usually Staph
Starts as a macule that fills with fluid or pus, ruptures and leaves yellow crusted exudate that spreads easily


Bullous impetigo

Staph aureus only
Rare, exfoliative toxin-producing strains
Intraepidermal lesion, begin as vesicles, enlarge to form flaccid bullae w/clear yellow fluid, fluid becomes dark, rupture, thin brown crust forms

Bullae containing exfoliatin but it does not disseminate, stays localized


Pyoderma Ecthyma

Ulcerative pyoderma down to the dermis
Greenish-yellow crust
Rarely infectious
Untreated impetigo, preexisting tissue damage, immunocompromised, poor hygiene, diabetes
Lower extremities, pigmentation scars from damage to dermis


Treatment of impetigo and ecthyma

Topical antibiotic: mupirocin
Systemic antibiotic: dicloxacillin, cephalexin; MRSA: TMP/SMX, clindamycin, doxycyclin, linezolid


General characteristics of Cellulitis and Erysipelas

Two types of similar skin infection
Dermis and Sub q tissue
Cellulitis: middle-aged and older adults
Erysipelas: young kids and old adults


Cellulitis risk factors and pathogens

skin lesions (varicella)
Chronic steroid use

S aureus:
Frequent pathogen
does not spread as fast as GAS

Acinetobacter baumannii:
g(-) aerobic rods to cocobacilli
Uncommon but specific
Assoc. with trauma, gunshot, venous catheters
Multi-drug resistant and pan-resistant

Pasteurella multocida:
g(-), mouths of dogs and cats
Purulent drainage

Aeromonas hydrophilia:
g(-) fresh water

Vibrio vulnificus:
g(-) salt water


Hallmark cellulitis manifestations

Uncomplicated, unnecrotizing inflammation, deeper dermis and sub q,
Heat, Erythema, Edema, Tenderness (skin becomes hot and swollen)


Other manifestations of cellulitis

orange peel appearance
Possible bullous, petechiae, ecchymoses


Cellulitis Diagnosis

2 Categories:

1) Small area, minimal pain, no systemic infection, responds well to treatment: no further workup needed

2) Extensive areas of involvement, spreading, underlying comorbidities; Lab workup required–may be more serious necrotizing fasciitis or myonecrosis


Cellulitis treatment

Avoid NSAIDS–mask indications of worsening disease, inhibit PMN and cytokine release

Elevate and immobilize
Keep skin moist
Antibiotics depending on purulent vs not

Reevaluate within 24-72 hours



A type of cellulitis caused by GAS primarily and S. aureus
Distinct borders as compared to cellulitis
Affects young and old


Erysipelas symptoms

Involves upper dermis and superficial lymphatics
Lesions raised above surrounding tissue
Clear line of demarcation
Involvement of the ear–significant because ear has no deeper sub q tissue so cellulitis doesn't usually affect the ears
Some systemic signs: fever, chills


Erysipelas distribution

Most commonly lower extremities
Face-10%–butterfly distribution


Erysipelas treatment

Elevation and immobilization
Skin kept moist and hydrated
Antibiotics: IV–ceftriaxone (beta-hemolytic strep), cefazolin (BHS and MSSA)
Followed by oral penicilin or amoxicilin
No macrolides (azithromycin, erythromycin, clarithromycin)