Skin and Soft Tissue Infections

Question 1

What is the most commonly infected soft tissue?

Answer 1

Skin

Question 2

Define Impetigo

Answer 2

Skin infection affecting the epidermis, usually staphylococcal

Question 3

Define Erysipelas

Answer 3

Skin infection of the epidermis, usually streptococcal

Question 4

Define Cellulitis

Answer 4

Skin infection of the dermis +/- subcutaneous fat

Either streptococcal or staphylococcal

Question 5

Define Furuncle

Answer 5

Deep infection of a hair follicle, commonly known as a ‘boil’
Usually staphylococcal

Question 6

Define Carbuncle

Answer 6

Connecting collection of furuncles

Question 7

Define Necrotising Fasciitis

Answer 7

Deep bacterial infection of the fascia +/- underlying muscle
Usually streptococcal or mixed bacteria
Often originates from pelvis, also associated with blunt trauma

Question 8

Name a typically commensal form of staphylococcus bacteria

Answer 8

Coagulase negative staphylococci- often colonise on the skin but remain commensal bacteria despite being pathogenic

Question 9

Describe the microbial factors that allow pathogenesis

Answer 9

Access: most bacteria that cause SSTI are already colonised on skin
Adherence: bacteria are well developed adhesion molecules (necessary for colonisation)
Multiplication: colonisation of skin or wounds may precede infection
Evasion: Staph catalyse enzyme can block free radicals (produced by neutrophils), Staph M protein can block complement
Resistance: Many SSTI causing bacteria are drug resistant
Damage: Affects epidermis, dermis and deeper tissues, may lead to septicaemia
Transmission: easily from person to person by skin to skin direct contact

Question 10

Risk factors for SSTIs

Answer 10

Direct inoculation (trauma, medical procedure, skin ulcers)
Previous colonisation (staph aureas, especially MRSA)
Poor hygiene
Immunosuppression (diabetes mellitus, renal failure)