Lecture 3 Skin Infections

Question 1

What are the defences of the skin?

Answer 1

Dry, acidic (organisms convert sebum to FA), salty (sweat) -> not inducive environment for bacteria to grow
Dead keratinised cells -> difficult to degrade, provides no nutrients so difficult to colonise
Sloughing of surface cells -> removes adhered bacteria on the surface layer
Normal flora -> competes for adherence sites and nutrients
Lysozymes, toxic lipids -> protects hair follicles, sweat glands
Skin associated lymphoid tissue (SALT) -> Langerhans cells combat bacteria and prevent them entering deeper tissue

Question 2

Types of skin infections?

Answer 2

1. Insect bites
2. Traumatic/surgical injury
3. Burns

Question 3

Which bacteria causes Lyme disease and what are the morphological characteristics and virulence factors of that bacteria?

Answer 3

Borrelia burgdorferi via ticks or lice
G- large spirochaete
Microaerophilic (requiring little free oxygen), fastidious, slow-growing

NO TOXINS
Antigenic variation to avoid IS
Outer surface proteins A to F

Question 4

What are the symptoms of Lyme disease?

Answer 4

Fever, headache, fatigue
Erythema migrants (rash) at insect bite site

Question 5

What are the subsequent disorders of Lyme disease?

Answer 5

Inflammatory disorder eg recurrent arthritis attacks

If there is dissemination to CNS may cause meningitis, myocarditis

Question 6

What are the types of infections of cuts and their respective bacteria?

Answer 6

Surgical wound infection: Staphylococcus aureus, Streptococcus pyogenes
Traumatic wound infection (deeper tissue, so must be facultative or anaerobic): Staphylococcus aureus, Clostridium perfringes

Question 7

Describe a burn injury

Answer 7

Moist (serous) and highly nutritious surface
Eschar: dead skin and debris on surface of deep burns, associated with microbes
Disturbance of physiological fluid and lost of electrolytes
Damages neutrophil function and immune response

Question 8

Distinguish between a non-invasive and invasive burn

Answer 8

Non-invasive: confined to eschar, eschar separates from underlying tissue, purulent exudate, systemic symptoms are mild

Invasive: deeper tissue damaged and organisms invade deeper, serious systemic symptoms (bloodstream, septicaemia)

Question 9

Name the most common burn pathogen, it’s morphological characteristics and virulence factors.

Answer 9

Pseudomonas aeruginosa

G- rod, opportunistic pathogen
Minimal requirements, predilection for moist burn environment

Extracellular protease (exotoxins): degrade proteins to adhere
Elastase/protease: degrade tissue to invade