DLA8, DLA10- Skin Overview and Infections

Question 1

list the 5 layers of epidermis

Answer 1

(superficial to deep)
-stratum corneum
(-stratum lucidum, thick skin only)
-stratum granulosum
-stratum spinosum
-stratum basale

Question 2

list the natural defense mechanisms of the skin

Answer 2

• keratin
• AMPs (antimicrobial peptides) host defense
• skin sloughing
• Sebum: low pH, lipids (sphinoid bases)
• Sweat: low pH, high salt, lysozymes (peptidoglycan disruption)

Question 3

(1) and (2) are common infections related to poor hygeine

Answer 3

• impetigo

- furuncles = clustered boils

Question 4

____ is a common disease contracted from beaches or soil in tropical areas

Answer 4

cutaneous larva migrans (nematodes, hookworms)

Question 5

primary skin infections are caused by (1) to affect (2); examples include: (3)

Answer 5

(primary pyodermas)
1- single pathogen
2- normal skin
3- S. aureus, β-hemolytis streptococci, coryneform bacteria

Question 6

Secondary skin infections are defined as (1), caused by (2).

Answer 6

(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

Question 7

describe mechanism of ‘athletes’s foot’

Answer 7

• 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-)

Question 8

compare macule, nodule, papule

Answer 8

• 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)

Question 9

define skin patch

Answer 9

• a macule >1 cm in diameter
• skin color alteration
• no elevation

Question 10

define a bulla/vesicle (includ subtypes)

Answer 10

• small, abnormal elevation of outer layer of skin enclosing watery liquid
• Blister/Vesicle = 1-5 mm in diameter
• Bullae > 5 mm in diameter

Question 11

examples of vesicle and bullae diseases

Answer 11

Vesicles: chickenpox (VVZ), oral herpes (HSV1), hand/foot/mouth disease

Bullae: bullous impetigo

Question 12

define a pustule and its associated diseases

Answer 12

• small circumscribed elevation of skin containing pus w/ inflamed base
• acne, chickenpox (VVZ), smallpox

Question 13

(T/F) pustules are always associated with hair follicles

Answer 13

F- they usually are, but not always

ex: folliculite, boils, chickenpox (VVZ)

Question 14

define wheal (include examples)

Answer 14

• localized area of edema, usually irregular and variable in size and color
• ex: hive, insect bite

Question 15

list the primary skin lesions

Answer 15

macule, papule, nodule, vesicle, bulla, pustule, wheal, plaque

Question 16

list the secondary skin lesions

Answer 16

scale, crust, fissure, ulcer

Question 17

define plaque (include examples)

Answer 17

• large, flat, elevated, solid surface

- ex: psoriasis

Question 18

define scale (include examples)

Answer 18

• thin/thick flake of skin varying in color
• secondary to desquamated, dead epithelium
• ex: dandruff

Question 19

define crust (include examples)

Answer 19

• dried residue of exudate

- ex: impetigo residue

Question 20

define fissure (include examples)

Answer 20

• linear crack in skin

- ex: athlete’s foot

Question 21

define ulcer (include examples)

Answer 21

• opening of skin caused by sloughing necrotic tissue
• extends past epidermis
• ex: pressure ulcer, stasis ulcer

Question 22

impetigo is a (primary/secondary) pyoderma caused by (2)

Answer 22

1- primary

2- S. aureus, Grp. A Strep

Question 23

cellulitis/erysipelas are a (primary/secondary) pyoderma caused by (2)

Answer 23

1- primary

2- Grp. A Strep

Question 24

folliculitis is a (primary/secondary) pyoderma caused by (2)

Answer 24

1- primary

2- S. aureus, pseudomonas aeruginosa

Question 25

erysipeloid is a (primary/secondary) pyoderma caused by (2)

Answer 25

1- primary

2- erysipelothrix rhusiopathiae

Question 26

erythrasma is a (primary/secondary) pyoderma caused by (2)

Answer 26

1- primary

2- corynebacterium minutissium

Question 27

intertrigo is a (primary/secondary) pyoderma caused by (2)

Answer 27

1- secondary

2- usual skin flora

Question 28

psuedofolliculitis of the beard is a (primary/secondary) pyoderma caused by (2)

Answer 28

1- secondary

2- usual skin flora

Question 29

furuncles/carbuncles are a (primary/secondary) pyoderma caused by (2)

Answer 29

1- primary

2- S. aureus

Question 30

describe differentiating between Streptococcus and Staphylococcus by microscopy

Answer 30

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

Question 31

Staphylococcus:

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

Answer 31

-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)

Question 32

what are and how are the Staphylococcus species divided

Answer 32

Coagulase+: S. aureus

Coagulase-: most remaining medically relevant Staph

Question 33

what are and how are the Streptococcus species divided [include where Group A species fall into]

Answer 33

• α-hemolytic (partial): pneumoniae, viridans
• β-hemolytic (complete): pyogenes (Group A, bactracin sensitive), agalactiae (grp. B, bact. resist.)
• γ-hemolytic (none): enterococcus

Question 34

S. pyogenes, aka (1), are (α/β/γ)-hemolytic and bacitracin (sensitive/resistant)

Answer 34

1- group A strep.
2- β-hemolytic
3- bacitracin sensitive

Question 35

describe the method and purpose of PYR test

Answer 35

(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

Question 36

describe the agars used for C. perfringes

Answer 36

• 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

Question 37

(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.

Answer 37

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

Question 38

how is a dermatophytic infection identified

Answer 38

• scraping skin scales / infected nails (aspirate if needed)

- mix sample with KOH on slide –> only the hyphae structure remains

Question 39

list the diagnostic tests for Mycobacterial skin infections

Answer 39

• 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

Question 40

describe the test used to determine erysipelothrix rhusiopathiae infection

Answer 40

(erysipeloid)

• H2S production test
• does microbe reduce S-containing compounds to Sulfides
• add Fe compounds –> sulfide production is positive if solution has black precipitate

Question 41

Bone and joint infections usually require (1) as investigation and (2) therapy over (3) amount of time

Answer 41

1- analysis of fluid in joint or bone by culture (infectious arthritis, osteomyelitis) [note- radiography will be helpful]
2- antimicrobial therapy
3- wks-mos