Lecture 14 - skin and soft tissue infection

Question 1

What is Cellulitis

When is it often found?

Answer 1

• Infection of dermis and sub-cutaneous tissue

- Often seen around injury site or deep abscess

Question 2

Inflammation response to bacterial infection

innate immune responses

Answer 2

-bacteria gets past skin barrier
-produces toxins, these damage tissues
-mast cells and macrophages become activated and send of further pro inflammatory cytokines and chemokines
(mast cells - release heparin and histamine) (macrophages can recognise PAMPs)
-vasodilation and increased permeability of blood vessels results
-nuertrophils can squeeze out of blood to site of infection
-platelets produce blood clots around bacteria to stop it getting into blood
-neutrophils fight the bacteria

PAMPS - can trigger proinflammatory cytokines

• Complement system activated in response to cell wall components on bacteria
• nuetrophils squeeze out of blood

Question 3

Streptococcus pyogens

Answer 3

gram positive
coci
cause SSTI, toxic shock syndrome, pharyngitits, rhuematic fever
group A antigen
15-20% of population have this colonisation in oropharynx
-can also colonise skin
-transmission by human contact
-infection rates higher - overcrowded houses, tropical areas

Question 4

How do they colonise

Answer 4

• Have proteins that bind to ECM
• capsule - hyaluronic acid - prevents opsonisation and phagocytosis
• M protein - penetrates the capsule, can interact with complement regulatro - stops opsoinsaiton by binding H factor

as toxins - streptolysis, ca paptidase, dnases, cep

Question 5

Spreading factors

Answer 5

to try and get into blood stream, proteases, lipases abd hyularonidases
streptokinase - to damage blod clots

Question 6

what is Necrotising fasciitis (flesh eating disease)

Answer 6

• Deep infection of skin, destruction of tissue and fascia
• development into severe systemic disease
• high mortality

Question 7

How to diagnose a skin infection?

Answer 7

• take a swab of purulent (pus containing) material

- cultivate and identify organism in micro lab

Question 8

treatment for SSTI
S.pyogenes

s,aureus

Answer 8

Penicilin , amyoxicilin

beta lactamase resistant penicilin - flucloxacillin (except for MRSA strains)

Question 9

How does penicillin work?

Answer 9

Binds to transpeptidase enzyme - and this stops the peptide cross links in bacteria cell wall
-results in a weak cell wall and cell lysis