Infections Of The Skin

Question 1

What are features of the skin as a defensive barrier?

Answer 1

\+ Epidermis: hard horny layer of cells 
\+ Surface is dry
\+ Constant sloughing
\+ Acidic pH
\+ Sweat secretion
\+ Rich blood and lymphatic supply
\+ Produces antimicrobial substances e.g
- fatty acids
- sebum
- defensins

Question 2

What are examples of normal microbiota?

Answer 2

+ Coagulase-negative Staphylococci

• Staphylococcus epidermidis
• Staphylococcus aureus

+ Streptococcus pyogenes

+ Propionibacterium acnes

+ Corynebacterium sp.

+ Candida sp.

Question 3

Where is the site of infection for ringworm?

Answer 3

Keratinised epithelium

Question 4

What is the site of infection for impetigo?

Answer 4

Epidermis

Question 5

Where is the site of infection for folliculitis?

Answer 5

Hair follicles

Question 6

Where is the site of infection for cellulitis?

Answer 6

Subcutaneous fat

Question 7

Where is the site of infection for necrotising fasciitis?

Answer 7

Fascia

Question 8

Where is the site of infection for gas gangrene?

Answer 8

Muscle

Question 9

What are the routes of infection?

Answer 9

Via:

+ Skin

• pores
• hair follicles

+ Wounds

• scratches
• cuts
• burns

+ Bites

• insects
• animals

Question 10

Name some bacterial infections of the skin

Answer 10

+ Staphylococcus aureus
+ Staphylococcus pyogenes
+ Pseudomonas aeruginosa
+ Myobacterium tuberculosis

SOME MAY BE TOXIN MEDIATED

Question 11

What are features of streptococcus pyogenes?

Answer 11

\+ Cocci morphology
\+ Grows in chains 
\+ Gram positive 
\+ Group A Streptococcus (GAS)
\+ Multiple virulence factors
\+ Beta-haemolytic

Question 12

What are features of staphylococcus aureus?

Answer 12

\+ Cocci morphology
\+ Grows in clusters 
\+ Gram positive
\+ Causes huge range of illnesses
\+ Antibiotic resistant strains
- MRSA
- VRSA
\+ Multiple virulence factors 
\+ Direct infection or effect of toxin

Question 13

What are features pseudomonas aeruginosa?

Answer 13

\+ Coccobacillus morphology 
\+ Gram negative
\+ Monotrichous flagellum
\+ Opportunistic pathogen 
\+ Colonises catheters etc.
\+ Produces exotoxin A

Question 14

What are different forms of skin lesions?

Answer 14

+ Macule

• raised
• red
• local inflammation

+ Papule

• raised
• red
• more marked inflammation

+ Vesicle
- small blister

+ Ulcer
- disruption of epithelium

Question 15

What is an abscess?

Answer 15

Collection of pus; pustule

Question 16

What is a (cutaneous) vesicle?

Answer 16

Blister; bullae (pl.); fluid filled sac

Question 17

What is pyoderma?

Answer 17

Pus-forming skin infection; cutaneous abscess

Question 18

What is impetigo?

Answer 18

Vesicles developing into rupturing pustules then forming dried crusts

Question 19

What is ecthyma?

Answer 19

Rupturing vesicles leading to erythematous lesions and dried crusts

Question 20

What is folliculitis?

Answer 20

Inflammation at hair follicle

Question 21

What is a furuncle?

Answer 21

Boil; deep folliculitis

Question 22

What is a carbuncle?

Answer 22

Collection of boils

Question 23

What is erysipelas?

Answer 23

Erythema and inflammation of superficial dermis

Question 24

What is cellulitis?

Answer 24

Erythematous inflammation affecting deeper dermis and subcutaneous fat

Question 25

What is acne?

Answer 25

Infection of sebaceous follicles

Question 26

What is necrotising fasciitis?

Answer 26

Cellulitis with necrosis affecting skin, deeper fascia and sometimes muscle

Question 27

What is dehiscence?

Answer 27

Wound rupture along surgical suture

Question 28

What are types of fungal infections?

Answer 28

\+ Dermatophytes
Tinea app.
- Tinea pedis
- Tinea corporis 
- Tinea cruris 

+ Yeast

• Candida albicans
• Malassezia furfur

Question 29

What are examples of viral infections of the skin?

Answer 29

+ Human papilloma viruses (HPV)
- warts

+ Herpes simplex virus 1 (HSV1)
- cold sores

+ Herpes simplex virus 2 (HSV2)
- genital warts

+ Varicella zoster virus (VZV)

• chicken pox
• shingles

+ Coxsackie A virus
- hand, foot and mouth disease

Question 30

Give an example of a parasite of the skin?

Answer 30

Sarcoptes scabei (mite)

Question 31

What does Sarcoptes scabei cause?

Answer 31

Scabies

Question 32

What are the features of scabies?

Answer 32

\+ Mite burrows into skin
\+ Female lays eggs 
\+ Infection is asymptomatic 
\+ Hypersensitivity may occur
\+ May lead to superinfection