DLA8, DLA10- Skin Overview and Infections Flashcards Preview

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Flashcards in DLA8, DLA10- Skin Overview and Infections Deck (41):

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

-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

-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


-Gram (+/-)
-catalase (+/-)
-oxidase (+/-)
-(aerobic/facultative anaerobic/obligate anaerobic)
-(high/moderate/low) salt tolerance

-non-motile (no flagella)
-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)


describe the test used to determine erysipelothrix rhusiopathiae infection

-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