Cutaneous Microbiology Flashcards
Cutaneous flora
prevent infection by pathogenic organisms
- hydrolysis of skin lipids in sebum to free FA –> toxic to some bacteria
- aerobic Gram+ cocci, Gram- bacteria, corneyform bacteria, yeast, parasites
- overgrwoth lead to inflammatory diseases
- transmitted by carrier without symptoms
- cultures must be interpreted in light of normal flora
Impetigo
Predominantly affects children
secondary impetiginization can affect any age group
- Non-bullous due to S. aureus and some times S. pyogenes
- compromise of skin barrier allows superficial infection
- yellow, honey-colored crust, vesicles, pustules, non-healing wound may suggest impetiginization
- Bullous due to S. aureus phage II type 71
- secreted toxins mediate disease by disrupting desmoglein
- occurs on intact and compromised skin
- flaccid bullae with prodrome of malaise, fever, diarrhea
- children appear non-toxic, rapid resolution
diagnosed via clinical presentation + culture of wound base or bulla fluid
treated by covering site (prevent transmission), topical abx for local, oral abx for generalized
Ecthyma
typically related to trauma and occurs at any age
- due to S. pyogenes or S. aureus
- begins with pustules and vesicles, ulcerations develop with thick, adherent crust and heals with scarring
- diagnosed via wound culture
- oral abx
Abscess, Furuncle, Carbuncle
Abscess: collection of pus with surrounding fibrous rxn
Furuncle: abscess that involves a hair follicle
Carbuncle: a collection of furuncles
- most common amound adolescents and YA
- risk factors are diabetes, immunosuppression, obesity, poor hygiene
-due to S. aureus, anaerobic bacteria in groin
- may occur at any site, favors sites of trauma or friction
- tender, red nodule that becomes fluctuant
- absence of systemic symptoms
- diagnosed via clinical & culture of purulent exudate
- treated by warm compresses, incision and drainage, oral abx if perinasal, large/recurrent, surrounding cellulitis, failure to respond
Erysipelas
Most commonly affects elderly patients
- due to S. pyogenes
- characterized by erythematous plaque with sharply demarcated border
- mainly affects face and lower extremities
- possible prodrome of fever, chills, malaise
- lymph destruction may result in recurrent infections
- diagnosed via clinical presentation
- treated via Abx
Erythrasma
Affects adult population
- caused by Corneybacterium minutissimum
- well-defined erythematous patches with fine scale
- involves axillae, inguinal folds, gluteal cleft, other moist sites
- generally asymptomatic
- diagnosed via Wood’s lamp exam w/ coral red fluoro
- treated with topical Abx or topical antifungals
Tinea Corporis, Capitis, Pedis, Cruris
Tinea capitis (head) most common in children Tinea corporis (body), pedis (feet) and cruris (groin) more common in adults Tinea unguium (nails) aka onychomycosis common in adults
- caused by dermatophytes (trichophyton, epidermophyton, microsporum spp.)
- infections anthropophilic, zoophilic, or geophilic
- capitis: white scaling patches w/ hair loss
- corporis: erythematous, annular scaling plaques
- cruris: red, macerated patches in groin but not scrotum
- pedis: variable presentation in plantar area, redness, scale, vesicles, pustules, interdigital maceration
- unguium: yellow subungual hyperkeratosis/white scale
- diagnosed via KOH examination w/ branching hyphae and culture for capitis and onychomycosis
- treated with topical antifungals (clotrimazole, terbinafine)
Pityriasis (tinea) versicolor
Infections usually after puberty, most common in YA
- caused by Malassezia furfur (yeast)
- transmitted via direct contact
- can be asymptomatic, macules and patches with fine, white, superficial scale –> scraping = more apparent
- pink in winter months (hypopigment in summer)
- diagnosed via KOH (spaghetti and meatballs)
- treated via antifungals, oral antifungals for extensive disease, wash skin twice monthly with selenium sulfide
Cutaneous candidiasis
Most common in summer/high humidity and exacerbated in obesity as skin folds = moist, warm envi (diaper dermatitis)
- caused by Candida yeast
- presents Intertrigo (erythematous patches with satellite papules and pustules, maceration, foul odor, scrotum)
- diaper dermatitis: red papules and plaques with erosions
- diagnosed via KOH, revealing pseudohyphae (yeast)
- treated with topical antifungals (clotrimazole, nystatin), NOT terbinafine
- zinc oxide paste may help protect the skin against chronic maceration
Seborrheic dermatitis
Affects infants
Herpes simplex (HSV)
HSV1 - oral, HSV2 - genital disease
-high incidence of subclinical infection
- primary infection - first exposure to virus
- latent infection - virus travels retrograde to DRG (dormant until triggered by immunosuppression, stress, UV)
- secondary infection - same location as primary
- transmitted via direct contact and less commonly fomites
- prodrome of tingling sensation, painful uniform vesicles on red base which becomes eroded and crusted (scalloped borders), lymphadenopathy may occur, EM
- diagnosed by clinical presentation, Tzank prep (multinucleated giant cells), serologic test for Ab, culture (low sensitivity), PCR
- treated with oral antivirals (acyclovir) - must treat w/in 48 hrs of symptoms onset to reduce symptoms but no cure, crusted lesions no longer infectious
Erythema multiforme (EM)
Recurrent, self-limited eruption of skin and/or oral mucosa
- may occur concurrently with clinical or subclinical HSV
- EM is rxn to underlying infection and HSV not present within skin lesions
- presents with targetoid macules
Varicella zoster (VZV)
Shingles - affects pple who had chicken pox and are immunosuppressed
- malaise and vesicles on erythematous base ]
- risk of postherpetic neuralgia (chronic pain) among elderly and immunosuppressed
- virus travels retrogate to DRG
- immunosuppression allows virus to go back to skin
- prodrome of tingling and pain with dermatomal painful vesicles, lymphadenopathy may be present
- diagnosed via clinical + Tzank prep (multinucleated GCs)
- treated with oral antivirals + VZV vaccine
Warts
Affects children and adults (lots of types of HPV)
- spread by direct contact
- HPV infects basal keratinocytes
- condyloma acuminata = warts affecting genital mucosae
- HPV 16, 18, 33, 35 risk for cervical cancer
- skin-colored papules with rough surface
- black dots represent thrombosed blood vessels
- flat warts with minimal scale vs. hyperkeratotic warts
- interuption of dermatoglyphs (fingerprints) ID residual
- diagnosed via clinical + acetowhite (vinegar) application + pap test
- treated via salicylic acid (daily), cryotherapy, immunotherapy, electrodessication and curettage, laser, HPV vaccine
Molluscum contagiosum
Affects children and adults
-considered an STD among adults
- spread via direct contact
- asymptomatic skin-colored papule with umbilicated center
- rarely pruritic
- diagnosed via clinical presentation
- treated with cryotherapy, curettage, immunotherapy, but also resolves spontaneously
Erythema Infectiosum (Fifth disease)
Most common among school age children
- spread through respiratory secretions
- caused by parvovirus B19
- children have rare prodrome of fever + malaise (1-2 days before rash), red patches on cheeks, lacy, reticulate patches after several days
- adults have prodrome of headache, fever, ab pain, may develop arthralgias (joint pain), risk of aplastic crisis, infection in pregnancy increases risk of hydrops fetalis
- diagnosed clinically, acute and convalescent serum test
- treatment is supportive, pregnant women should be isolated
Scabies
Affects adults and children
common w/ individuals living in close quarters
crusted (norwegian) scabies affect pple w/ neurologic disorders or immunosuppression
- due to Sarcoptes scabei mite that lives in stratum corneum
- mites don’t survive >2-3 days away from human skin
- causes hypersensitivity rxn, may be asympt. for 2-6 weeks
- intense itching, particularly at night, inflam papules, vesicles and burrows
- affects web spaces, wrists, waistline, sides of hands/feet, penis, scrotum & nipples
- crusted scabies - thick crusting of hands and feet
- diagnosed via scabies prep (mites, eggs, scybala)
- treated with topical antiscabetics (permetrin 5% cream), sulfur in petrolatum (pregnant women, infants)
- oral antiscabetics (ivermectin) - resistance, epidemics
- environmental controls
KOH examination
Scrape scaling edge of plaque or underside of vesicle with scalpel
- place scale on glass slide
- apply 1-2 drops of KOH and cover slip
- gently heat fix
- wait several minutes and observe under microscope for hyphae and/or spores
Tzanck Prep
scrap base of vesicle with scalpel
place fluid on glass slide and allow air dry
apply Tzanck stain and gently rinse off
observe under microscope for multinucleated giant cells
Scabies prep
scrape end of burrow with scalpel down to bleeding
place cells on glass slide
apply 1-2 drops of mineral oil
observe under microscope for mites, eggs or scybala
