Microbiology of the Skin Flashcards
Staph aureus
Aerobic cocci
Impetigo, SSSS, abscess
Corynebacterium minutissimum
Coryneform bacteria
Erythrasma
Proprionobacterium acnes
Coryneform bacteria
Acne vulgaris
Malassezia furfur
Yeast
Pityriasis versicolor and folliculitis
Demodex mites
Parasite
Rosacea
Impetigo (cause, population, affected skin layer, 2 types, sxs, tx)
Due to staph aureus.
More common in children.
Disrupts epidermis.
Non-bullous type – Honey-colored crusting. Vesicles and pustules. Staph aureus > strep pyogenes.
Bullous type – due to staph aureus phage II toxin disrupting desmoglein 1 → blister. Acts as localized form of SSSS. Prodrome of malaise, fever, diarrhea. Flaccid bullae. Most common in neonates.
Tx – cover affected site to prevent spread, topical antibiotics (mupirocin), or oral antibiotics for high risk patients.
Ecthyma (cause, affected skin layer, sxs, tx)
Strep pyogenes or staph aureaus. Follows trauma. Infects dermis. Painful ulceration, crusting, and heals w/ scarring. Tx w/ oral abx.
Abscess (sxs, cause, affected population, risk factors, often mistaken for, tx)
Collection of pus w/ surrounding fibrous reaction. Tender red nodule that becomes fluctuant (full of pus)
Staph aureus most common cause.
Common in adolescents and young adults.
Risk factors include diabetes, old age, immunosuppression, obesity, uncleanliness
Often mistaken for ruptured epidermoid cyst.
Tx – warm compresses, incision / drainage, oral antibiotics
Furuncle
Abscess that involves hair follicles
Carbuncle
Collection of furuncles
Erysipelas (Cause, affected skin layer, sxs, affected population, tx)
Due to strep pyogenes. Infection of dermis → red plaque w/ sharp borders. Fever, chills, malaise. Commonly affects elderly px. Tx w/ oral antibiotic.
Erythrasma (Cause, affected skin layer, sxs, diagnostic tool, tx)
Overgrowth of normal flora cornyebacterium minutissimum infects epidermis.
Well-defined red patches w/ red scale. Affects moist areas (skin folds, intertrigo). Most often in groin, sometimes toes. Often asymptomatic.
Wood’s lamp exam shows coral red fluorescence
Tx includes topical antibiotics or antifungal agents (works via anti-inflammatory effect)
Tinea infections (cause, source, diagnostic tool, tx)
Dermatophytes (TEM): trichophyton, epidermophyton, and microsporum
Source: anthropophilic, zoophilic, geophilic (soil)
Zoophilic transmission may cause a kerion (massive inflammation of hair follicles)
Diagnosed via KOH. Long branching (septate) hyphae w/ transverse areas of pallor.
Tx w/ topical antifungals (focal) or oral antifungals (widespread or hair follicles)
Tinea capitis
Head
White scaling patches w/ hair loss.
Common in kids
Tinea corporis
Body
Red scaling plaques w/ annular configuration
Tinea pedis
Feet
Red and scale w/ extension to lateral feet (moccasin distribution)
Plantar vesicles / pustules, and interdigital maceration
Tinea cruris
Groin
Spares scrotum, unlike intertrigo
Tinea unguium / onychomyosis
Nails
Yellow subungual hyperkeratosis or white scale
Pityriasis (Tinea) Versicolor (cause, population, sxs, diagnosis, tx, prevention)
Due to malassezia fufur (yeast).
Common among young adults.
Macules / patches w/ fine, white, superficial scale. Pink in winter. Hypopigmented (doesn’t tan) in summer.
KOH shows little clusters of spores w/ short pseudohyphae. “Spaghetti and meatballs”
Tx – topical antifungals (focal) or oral antifungals (widespread)
Oral – take 2 tablets, wait hour, exercise to sweat, rinse skin after 4 hrs, repeat in a week. Risk of hepatotoxicity.
Prevention includes selenium sulfide shampoo (selsum blue)
Seborrheic Dermatitis (cause, sxs, location, population, risk factors, tx)
Possibly due to pityrosporum yeast.
Presentation: yellow, greasy scale w/ or w/o erythema. Possible papules or maceration. Affects scalp, glabella (b/w eyebrows), alar creases (nose), chin, chest, and inguinal folds. Affects infants and adults.
HIV and Parkinson’s are risk factors.
Tx – Topical antifungals, weak topical steroid, anti-seborrheic shampoo (selenium sulfide). Sxs will improve, but it is never cured.
Cutaneous candidiasis (cause, sxs, worsening factors, diagnostic, tx)
Due to candida (albicans) yeast.
Intertrigo – red patches w/ satellite papules / pustules, maceration, foul odor, and DOES affect scrotum
Diaper dermatitis – red papules / plaques w/ erosion.
Worse w/ obesity (more skin folds) and humid weather.
KOH shows pseudohyphae (nonseptate chains of yeast)
Tx w/ topical antifungals or barrier pastes (zinc oxide)
Intertrigo
Sx of cutaneous candidiasis
Red patches w/ satellite papules / pustules, maceration, foul odor, and DOES affect scrotum
Diaper dermatitis
Sx of cutaneous candidiasis
Red papules / plaques w/ erosion. Exacerbated by humid weather.
Herpes simplex virus (types, prodrome, sxs, diagnostic, tx, associated disease)
1 is oral. 2 is genital.
High incidence of subclinical infection. Can still transmit while asymptomatic.
Sx include prodrome of tingling and then pain. Vesicles, hemorrhagic crust, scalloped border, palpable lymph nodes. No longer infectious when crust develops.
Diagnosed w/ Tzanck prep (nuclei die and coalesce), HSV1 /2 antibodies in serum, culture, and PCR
Tx – topical antivirals don’t work well. Oral antivirals used for 6+ outbreaks per year. Reduces transmission. Must be used w/in 48 hrs of sxs.
Associated w/ Erythema Multiforme
