Skin Infections Flashcards
Staph. aureus
Superficial infections like boils, abscesses and serious toxin-mediated disease
- scalded skin syndrome (results from exfoliative toxins A and B destruction of the intercellular connections and separation of the top layers of the epidermis)
- toxic shock syndrome (toxic shock syndrome toxin 1 (TSST-1) causes a diffuse macular erythematous rash followed by desquamation of the skin, particularly the soles and palms.)
Strept. pyogenes
- M proteins are important virulence factors which inhibit opsonization and cause resistance to phagocytosis; other important surface components are lipoteichoic acids and F proteins.
- Lysogenic strains produce pyrogenic exotoxins (streptokinase and streptolysin O and S) and hyaluronidase that help the organism spread.
- Can produce a toxic shock syndrome.
- Most skin infections are acute, but glomermulonephritis and rheumatic fever are potential systemic manifestations of infection and take a while to develop.
P. aeruginosa
Often associated with hot tubs and can cause epidermal infections and Mycobacterial species) can cause granulomatus disease.
Mycobacterium leprae
Causes leprosy, characterized by skin lesions and nerve damage.
Mycobacterium marium
Associated with water and marine organisms and result in disease follow minor trauma.
Malassazia furfur
A superficial/cutaneous mycoses that causes pityriasis, a common infection involving plaques on the trunk or proximal part of limbs.
Trichophyton, Epidermophyton, and Microsporium species
Cutaneous dermatophytes are spread by arthrospores from organisms in the soil or from contact with infected humans or animals. They love keratin and infect keratinized structures (skin, hair, and nails).
Sporotrichosis (Sporothrix schenckii)
Caused by a dimorphic fungus (Sporothrix schenckii) found in hay, moss, soil, and decaying vegetation; conidia and yeast cells bind to extracellular matrix proteins following entry after trauma caused by thorns or other agents to the skin of gardeners, farmers, rural laborers, and florists.
Mucocutaneous lesions caused by localized virus infection
Human papilloma virus (HPV) which infects only the basal layers of the skin or mucosa and causes warts
.Two poxviruses molluscum contagiosum virus and orf virus also cause localized disease.
How do viruses infect the dermis/cause rashes?
They can arrive via circulating microbes, toxin, or immune complex.
If microbe grows in the epithelium, a papilloma will form (wart)
OR
A macule can form from immune response. A papule can form if raised elevation. A vesicle can form if the microbes invade the epithelim (HSV, VZV). If epithelim ruptures, an ulcer forms.
Vesicular Lesions
Herpes simplex virus (HSV)
Varicella-zoster virus (VZV) (chickenpox),
Coxsackie A viruses (herpangina and hand, foot, and mouth disease)
HSV and VZV cause latent infections which can be activated at a later time.
Maculopapular lesions
Human parvovirus B-19 (erythema infectiosum, Fifth Disease)
Human herpes virus type 6 (roseola)
Measles virus
Rubella virus
ECHO viruses
Dengue virus
Smallpox virus.
Rickettsial Infections
- Rocky Mountain Spotted Fever (Rickettsia rickettsi)
- Typhus (Rickettsia typhi and prowazekii)
Transferred by ticks and fleas and lice respectively (zoonotic diseases) and infect vascular endothelial cells, kill them which causes leakage of blood that results in a skin rash.
“swimmers itch”
Schistosome infection which causes “swimmers itch” is contracted from water populated by aquatic birds.
Clostridia perfringes
Found in the soil and human and animal feces invade tramatized skin, multiply in subcutaneous tissue causing a cellulitis, and then infect muscle where they produce alpha toxin-mediated necrosis and bubbles of gas.
