Derm micro -Saviola Flashcards
What are the 2 most common bacterial causes of skin infections? What are their characteristics?
S. aureus=gram + clusters, catalase +, coagulase +, beta hemolytic, mannitol fermenting
S. pyogenes (Group A strep) =gram +, catalase -, beta hemolytic, bacitracin sensitive
What are the 2 main virulence factors of S. aureus that allow for derm infections?
- Panton-valentine leukocidin (PVL)==> gets into host cell membrane and creates a bore and causes the cell to lyse
- protein A =aggregation ==> evade phagocytosis and important in biofilm formation
What are the 2 main virulence factors of S. progenies (GAS) that allow for derm infections?
- M protein =evade phagocytosis
- Superantigens =streptococcal pyrogenic exotoxins
What is the cause of Acne vulgaris?
- increase in sebum released by sebaceous glands after puberty
- smal cysts in hair follicles from blockage of orifices by retention of sebum
- microaerophilic bacteria cause inflammation in the cyst
- P. acnes produces CAMP factor (acts with S. aureus beta hemolysin to cause cytolysis)
What is erysipelas? What is the most common cause and site of infection?
- type of superficial cellulitis with lymphatic involvement, dermis, and uppermost subcutaneous tissue
- febrile
- S. pyogenes
- face or lower extremities
What bacteria causes Bullous Impetigo? What virulence factor allows this?
S. aureus
-Exfoliative toxins (Epidermolytic toxin A and B) cleave desmoglein 1 –> lose adhesiveness —> blister/boil
How is S. aureus typed? How is S. pyogenes typed?
S. aureus is typed based on phage
S. pyogenes is typed based on M protein
What causes Staphylococcal Scalded Skin Syndrome?
- S. aureus exfoliative toxin (Epidermolytic toxin A and B)
- enters circulation ==> more wide spread sloughing off than in bullous impetigo
What causes Toxic Shock Syndrome (2)? How? What is the skin rash and desquamation due to?
- S. aureus that produces TSST-1
- ->superantigen binds to MHC II and T cell receptor nonspecifically ==> activate a lot of T cells
or
-Streptococci producing streptococcal pyrogenic exotoxins (super antigen) and types M1 and M3 may be overrepresented in this disease
-desquamation due to immune reaction damaging the skin
What other serious infections can group A streptococci cause?
- necrotizing fasciitis (pyrogenic exotoxins –> hypotension and death)
- Scarlet fever (exotoxin mediated)
What are maculopapular rashes generally due to? Are the viruses present in the rash?
- immune response
- viruses not present in the rash
What is measles due to? What is an important complication?
- Paramyxovirus (enveloped - ssRNA virus)
- rash due to the presence of antibody and immune reaction
- can cause subacute sclerosing pan encephalitis 6-7 years after disease –> death
What is Rubella?
-Togavirus (enveloped + ssRNA)
What virus causes Erythema Infectiosum? Where does this virus replicate?
Parvovirus B19
replicated in rapidly dividing erythroid precursors
What causes Roseola infantum? What are the symptoms?
HHV6 (large enveloped dsDNA virus)
-3-5 days of high fever followed by a maculopapular rash
Are viruses typically present in the vesicles in vesicular exanthema? What are 3 examples of this?
Yes!
(fluid in the vesicle can transmit the virus to others)
- Varicella -Zoster (chicken pox and shingles)
- Hand foot and mouth disease
- Variola (smallpox)
What kind of virus causes Varicella-zoster virus?
- herpesviridae family
- enveloped dsDNA virus
What virus is a large “brick-shaped” (dumbbell shaped core) virus that replicates in the cytoplasm of the host cell? What type of rash pattern is associated with this?
- Variola (smallpox)
- centrifugal pattern of rash on extremities
- high fever
How does the rash of Variola (smallpox) differ from that of Varicella (chickenpox)?
Variola=centrfugal (on head and extremities more
Varicella=more on chest
What causes Hand Foot and Mouth disease? How is this transmitted?
- Coxsackie A virus (Picornavirus)
- fecal oral or respiratory
Which 3 viruses infect the skin and remain in that local area?
- Herpes simplex virus
- Human papilloma virus (naked icosahedral dsDNA)
- Molluscum contagiousum
What do the the lesions of Molluscum contagiousum virus look like?
- smooth firm shiny flesh colored to pearly white hemispheric papules with umbilicated (indented) centers
- confined to the skin and mucous membranes.
- Pox family virus
- seen in kids and wrestlers a lot
What form do dimorphic fungi take in the environment? In human tissue?
environment=mold
body=yeast
What component of fungal membranes is different from human cell membranes? What is their cell wall made of?
- fungi have Ergosterol in their membranes
- cell wall contains chitin, glucan and mannoproteins (no peptidoglycan)
What test should be used to look for fungi?
KOH prep
Where are superficial mycoses found? Do they cause much inflammation? What are some examples? (2)
- limited to the outermost (cornified) layers of the skin and hair.
- no inflammation
- Pityriasis Versicolor (spaghetti and meatballs)
- Tinea nigra
Where are cutaneous mycoses found? What is another name for these? What do these organisms normally express? What are some examples?
- Dermatophytes
- infections that are deeper in the epidermis, hair, and nails but restricted to the keratinized layers of the skin.
- express keratinases that break down keratin
- Tinea capitis, tinea manus, tinea unguium, tinea corporis
- tinea pedia (athletes foot)
- tinea cruris (jock itch)
Where are subcutaneous mycoses found? What is an example of this? How does it spread?
- involving the dermis, subcutaneous tissues, muscle and fascia
- Sporotrichosis (dimorphic fungus)
- spreads through lymphatics
