Microbiology of the Skin Flashcards Preview

Dermatology > Microbiology of the Skin > Flashcards

Flashcards in Microbiology of the Skin Deck (35):

Staph aureus

Aerobic cocci
Impetigo, SSSS, abscess


Corynebacterium minutissimum

Coryneform bacteria


Proprionobacterium acnes

Coryneform bacteria
Acne vulgaris


Malassezia furfur

Pityriasis versicolor and folliculitis


Demodex mites



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



Abscess that involves hair follicles



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

White scaling patches w/ hair loss.
Common in kids


Tinea corporis

Red scaling plaques w/ annular configuration


Tinea pedis

Red and scale w/ extension to lateral feet (moccasin distribution)
Plantar vesicles / pustules, and interdigital maceration


Tinea cruris

Spares scrotum, unlike intertrigo


Tinea unguium / onychomyosis

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)



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


Erythema Multiforme (association, sxs)

Reactive skin eruption related to herpes, but no virus in these lesions. Targetoid lesions that are centrally erythemous. Often in mouth or genital skin. Recurrent.


Varicella Zoster Virus / Shingles (cause, population, sxs, diagnostic, tx, prevention)

Reactivation of latent infection from DRG. Can be caused by prior primary varicella (chicken pox).
Common in elderly.
Post-herpetic neuralgia (chronic pain after lesion has healed) is rare complication.
Diagnosed w/ Tzanck prep.
Tx w/ oral antivirals.
Vaccine prevents.


Human Papilloma Virus / HPV (affected skin layer, sxs, types, tx)

Infects basal keratinocytes.
Verruca vulgaris = wart
Condyloma acuminata = genital wart
HPV 6 / 11 cause genital warts.
HPV 16, 18, 33, and 35 are high risk for oral, cervical, anal, vaginal, vulvar, and penile cancers, as well as squamous cell carcinoma (SCC).
Tx w/ salicylic acid, cryotherapy, immunotherapy, surgical removal (cut or laser), or prevent w/ vaccine.


Verruca vulgaris

Wart on normal skin


Condyloma acuminata

Genital wart


Which HPV viruses cause genital warts?

6 and 11


Which HPV viruses cause cancer?

16, 18, 33, and 35


Molluscum contagiosum

Umbilicated papule.
STD in adults. Normal skin virus in children. Asymptomatic and resolves on own.


Erythema Infectiosum / 5th Disease (cause, transmission, sxs [adult vs child], tx)

Due to parvovirus B19.
More common in children.
Spread via respiratory secretions.
Kids – “slapped cheek” (red patches) and lacy, reticulate patches.
Adults present w/ prodrome of fever, headache, and abd pain. Also causes arthralgia, aplastic crisis (immature RBCs), and hydrops fetalis.
No tx. Avoid contact w/ pregnant women. No longer infectious once rash occurs.


Scabies (cause, affected skin layer, population, sxs, diagnostic, tx)

Due to sarcoptes scabei infecting corneum. Common in individuals living in close contact (adults and children).
Intense itching, papules, vesicles, and burrows (linear tracks)
Crusted (Norwegian) scabies – affects people w/ immunosuppresion, neurologic, or mental disorders. Thick crusting of hands / feet.
When scraping for test, locate black burrow. Mineral oil prep shows mites, eggs, and scabella (poop).
Tx – Treat all family members w/ topical / oral antiscabetics from neck-down. Rinse off in morning. Washing bedding / clothes (fomites) also important. Mites only live outside skin for 2-3 days.


Crusted / Norwegian scabies (population and sxs)

Affects people w/ immunosuppresion, neurologic, or mental disorders.
Thick crusting of hands / feet.