Skin & Soft Tissue Infections

Question 1

What are some bacterial skin infections and their common bacterial organism? (staph or strep)

Answer 1

Staphylococcus:
Impetigo
Furuncle - deep infection of a hair follicle
Carbuncle

Streptococcus:
Erysipelas - epidermis infection
Necrotising fasciitis - deep infection of fascia +/- muscle

Cellulitis either staph or strep

Question 2

Define pathogen and infection

Outline 2 microbial interactions

Answer 2

Pathogen = microbe able to cause disease
Infection = when the invasion and multiplication of microbes in an area of the body where they're not normally present and leads to disease

Commensal = symbiotic relationship where one derives some benefit
Colonisation = when a microbe grows on another without causing disease

Question 3

What microbe normally colonises our skin? how without causing disease?

Answer 3

Staphylococcus species -> Staph. Epidermidis lack coagulase enzyme and colonise nearly all human skin

Staphylococcus Aureus found in axilla/groin and pathogen if invades skin

Colonisation relationship requires break in skin to invade

De-colonisation treatment sterilises the skin

Question 4

What are risk factors for SSTIs?

Answer 4

Direct inoculation -> trauma, medical procedures, skin ulcers
Previous colonisation -> poor hygiene, Staph Aureus, MRSA
Immunosuppression -> diabetes mellitus, renal failure

Question 5

What microbiology samples can be taken?

Answer 5

Swabs -> pus, skin, nose, throat
Body fluids -> pus, vesicle fluid, blood
Body tissues -> biopsies

Question 6

Which antibiotics are used for Staph Aureus or Staph species skin infections, or opportunistic infections?

Answer 6

Staph aureus - usually resistance eg MRSA -> Flucloxacillin

Staph species - Penicillin

Opportunistic infections (eg in diabetic ulcers) -> Co-Amoxiclav

Question 7

What are the stages of bacterial pathogenesis?

Answer 7

Access - most bacteria found on skin as colonisers
Adherence - adhesin molecules
Invasion - most need skin break
Multiplication - colonisation of skin/wounds may precede infection
Evasion - Staph Catalase blocks free radicals, Staph M blocks complement
Resistance - many bacteria causing SSTI have drug resistance (eg MRSA)
Damage - affects epidermis, dermis and maybe deeper tissues
Transmission - easily passed from skin by direct contact

Question 8

What’s the basic underlying pathology of psoriasis?

Answer 8

Reduces the amount of time keratinocytes take to move from basal to cornfield layer

Question 9

What are coagulase negative staphylococci?

Answer 9

Staph species that aren’t Staph.Aureus eg Staphylococcus Epidermidis
Normally commensal bacteria and colonise human skin (only cause infections if reach prosthetic material)

Question 10

What’s the role of Staph Aureus on our skin and causing infections?

Answer 10

Normally considered a pathogen
May colonise skin if poor hygiene/abnormal skin
But still needs to invade and multiply to cause infection so often remains commensal and skin can be de-colonised to sterilise it

Question 11

How are lesions on the skin clinically described?

Answer 11

Shape
Size
Distribution
Edge
Colour
Surface

Question 12

What can Aciclovir be used for?

Answer 12

Viral skin infections eg herpes, chickenpox, shingles

Question 13

What are superficial skin infections treated with?

Answer 13

eg Impetigo

Topical Fuscidin

Question 14

Which antibiotic best targets Staphylococcus Aureus?

Answer 14

Flucloxacillin

Usually MRSA resistant

Question 15

Which antibiotics best targets Streptococcus species?

Answer 15

Rarely resistant to antibiotics so Penicillin usually works fine

Question 16

What type of antibiotics are good for opportunistic bacterial infections? Eg diabetic ulcers

Answer 16

Often polymicrobial so Co-Amoxiclav

Question 17

What’s used for fungal infections?

Answer 17

Topical Terbinafine as they’re usually superficial and rarely resistance to antimicrobials