DLA8, DLA10- Skin Overview and Infections Flashcards
list the 5 layers of epidermis
(superficial to deep) -stratum corneum (-stratum lucidum, thick skin only) -stratum granulosum -stratum spinosum -stratum basale
list the natural defense mechanisms of the skin
- keratin
- AMPs (antimicrobial peptides) host defense
- skin sloughing
- Sebum: low pH, lipids (sphinoid bases)
- Sweat: low pH, high salt, lysozymes (peptidoglycan disruption)
(1) and (2) are common infections related to poor hygeine
- impetigo
- furuncles = clustered boils
____ is a common disease contracted from beaches or soil in tropical areas
cutaneous larva migrans (nematodes, hookworms)
primary skin infections are caused by (1) to affect (2); examples include: (3)
(primary pyodermas)
1- single pathogen
2- normal skin
3- S. aureus, β-hemolytis streptococci, coryneform bacteria
Secondary skin infections are defined as (1), caused by (2).
(secondary pyoderma)
1- infection of existing skin lesion (ex. insect bites, scratching, cracks, etc)
2- mix of infectious and non-infectious causes: scabies, psoriasis, poison ivy, atopic dermatitis, eczema, herpeticum, kerion
describe mechanism of ‘athletes’s foot’
- toe web infection – secondary pyoderma
- 1st thought to only be fungal infection
- Now thought dermatophytes (fungi) first must cause skin damage
- this allows bacterial growth of coryneform bacteria and brevibacterium (& Gram-)
compare macule, nodule, papule
- Macule: patch of skin altered in color, no elevation —- if >1cm diameter = patch
- Papule: small, solid, conical elevation of skin
- Nodule (tumor): small mass, rounded/irregular shape, palpable (slightly larger and extend deeper than papules)
define skin patch
- a macule >1 cm in diameter
- skin color alteration
- no elevation
define a bulla/vesicle (includ subtypes)
- small, abnormal elevation of outer layer of skin enclosing watery liquid
- Blister/Vesicle = 1-5 mm in diameter
- Bullae > 5 mm in diameter
examples of vesicle and bullae diseases
Vesicles: chickenpox (VVZ), oral herpes (HSV1), hand/foot/mouth disease
Bullae: bullous impetigo
define a pustule and its associated diseases
- small circumscribed elevation of skin containing pus w/ inflamed base
- acne, chickenpox (VVZ), smallpox
(T/F) pustules are always associated with hair follicles
F- they usually are, but not always
ex: folliculite, boils, chickenpox (VVZ)
define wheal (include examples)
- localized area of edema, usually irregular and variable in size and color
- ex: hive, insect bite
list the primary skin lesions
macule, papule, nodule, vesicle, bulla, pustule, wheal, plaque
list the secondary skin lesions
scale, crust, fissure, ulcer
define plaque (include examples)
- large, flat, elevated, solid surface
- ex: psoriasis
define scale (include examples)
- thin/thick flake of skin varying in color
- secondary to desquamated, dead epithelium
- ex: dandruff
define crust (include examples)
- dried residue of exudate
- ex: impetigo residue
define fissure (include examples)
- linear crack in skin
- ex: athlete’s foot
define ulcer (include examples)
- opening of skin caused by sloughing necrotic tissue
- extends past epidermis
- ex: pressure ulcer, stasis ulcer
impetigo is a (primary/secondary) pyoderma caused by (2)
1- primary
2- S. aureus, Grp. A Strep
cellulitis/erysipelas are a (primary/secondary) pyoderma caused by (2)
1- primary
2- Grp. A Strep
folliculitis is a (primary/secondary) pyoderma caused by (2)
1- primary
2- S. aureus, pseudomonas aeruginosa
erysipeloid is a (primary/secondary) pyoderma caused by (2)
1- primary
2- erysipelothrix rhusiopathiae
erythrasma is a (primary/secondary) pyoderma caused by (2)
1- primary
2- corynebacterium minutissium
intertrigo is a (primary/secondary) pyoderma caused by (2)
1- secondary
2- usual skin flora
psuedofolliculitis of the beard is a (primary/secondary) pyoderma caused by (2)
1- secondary
2- usual skin flora
furuncles/carbuncles are a (primary/secondary) pyoderma caused by (2)
1- primary
2- S. aureus
describe differentiating between Streptococcus and Staphylococcus by microscopy
Staph (aureus): Gram+, grape-like clusters, Catalase+, yellow pigment on blood agar (β-hemolytic), penicillin G resistant
Strep (group A, S. pyogenes): Gram+, chain arrangement, Catalase-, no pigment production (although β-hemolysis), penicillin G sensitive
Staphylococcus:
- Gram (+/-)
- (non-/motile)
- catalase (+/-)
- oxidase (+/-)
- (aerobic/facultative anaerobic/obligate anaerobic)
- (high/moderate/low) salt tolerance
-Gram+
-non-motile (no flagella)
-catalase+
-oxidase-
-aerobic, some are facultative anaerobic
-high salt tolerance (mannitol salt+, good for sweaty skin)
(some are β-hemolytic on blood agar)
what are and how are the Staphylococcus species divided
Coagulase+: S. aureus
Coagulase-: most remaining medically relevant Staph
what are and how are the Streptococcus species divided [include where Group A species fall into]
- α-hemolytic (partial): pneumoniae, viridans
- β-hemolytic (complete): pyogenes (Group A, bactracin sensitive), agalactiae (grp. B, bact. resist.)
- γ-hemolytic (none): enterococcus
S. pyogenes, aka (1), are (α/β/γ)-hemolytic and bacitracin (sensitive/resistant)
1- group A strep.
2- β-hemolytic
3- bacitracin sensitive
describe the method and purpose of PYR test
(pyrrolidonyl arylamidase)
- identification of β-hemolytic Group A/S. pyogenes (+) and enterococci
- Note: β-hemolysis –> PYR => + for grp.A/S. pyogenes (bacitracin sensitive) and - for grp. B/S. agalactiae (bacitracin resistant)
- positive test is bright red, negative is no color change/rxn
describe the agars used for C. perfringes
- Blood agar: β-hemolysis with outer layer of α-hemolysis (double zone)
- EYA (egg yolk agar): 1) Lecithinase (phospholipase toxin) => white opaque zone around colonies, 2) Lipase => pearly, iridescent sheen to colonies
(1) test is used to differentiate C. perfringes after a (2)+ test on a (3) agar. The (3) plates is divided in halves with (4), and a positive result is if (5) occurs.
1- Nagler test 2- lecithinase+ (clostridium spp) 3- EYA (egg yolk agar) 4- type A antitoxin (and a side w/o) 5- toxin is produced on non-antitoxin side, seen as cloudiness
how is a dermatophytic infection identified
- scraping skin scales / infected nails (aspirate if needed)
- mix sample with KOH on slide –> only the hyphae structure remains
list the diagnostic tests for Mycobacterial skin infections
- Ziehl-Neelson / Acid-fast stain
- growth on Lowenstein-Jensen agar (4-8 wks)
- growth speed
- pigment production (light/dark)
- sequencing of rpoB, hsp65 genes (gold standard)
- NAAT
describe the test used to determine erysipelothrix rhusiopathiae infection
(erysipeloid)
- H2S production test
- does microbe reduce S-containing compounds to Sulfides
- add Fe compounds –> sulfide production is positive if solution has black precipitate
Bone and joint infections usually require (1) as investigation and (2) therapy over (3) amount of time
1- analysis of fluid in joint or bone by culture (infectious arthritis, osteomyelitis) [note- radiography will be helpful]
2- antimicrobial therapy
3- wks-mos
