Lecture 4 - Skin and Soft Tissue Infection

Question 1

Cellulitis?

Answer 1

infection of dermis and subcutaneous tissue, often seen around injury site or deep abscess

Question 2

Erysepelas?

Answer 2

acute infection of the upper dermis and superficial lymphatics

Question 3

Inflammation in response to bacterial infection?

Answer 3

bacteria enters wound, platelets release blood-clotting proteins @ site, mast cells secrete factors (histamine) for vasodilation and vasoconstriction (recruitment), neutrophils kill and degrade pathogens, neutrophils and macrophages phagocytose pathogens, macrophages secrete cytokines that attract immune cells and activate tissue repair, response continues until repaired

Question 4

Innate immune response?

Answer 4

non-specific, immediate, short-lasting - pathogen-associated molecular patterns recognised by pattern recognition receptors (e.g. LPS gram -ve, PGN gram +ve) -> secretion of pro-inflammatory cytokines

Question 5

Cytokines increasing vessel permeability of neutrophils?

Answer 5

increased adhesive E-selectin proteins of and loosening gaps between basement membrane endothelium, -> follow chemotactic gradient

Question 6

Complement system (general)?

Answer 6

3 different pathways, produce C3b for opsonisation and C5a for migration aid

Question 7

Lancefield classification by Sero-typing?

Answer 7

specific antibody against group A antigen will bind and stain Group A streptococcus

Question 8

Strep attachment to skin?

Answer 8

MSCRAMMS - cell wall attached adhesions, specific binding to host extracellular matrix proteins (fibronectin, elastin etc.) - also prevents C3b opsonisation

Question 9

Hyaluronic acid capsule?

Answer 9

prevents opsonisation and phagocytosis

Question 10

Toxins secreted by s. pyogenus?

Answer 10

streptolysins, C5a peptidase, DNases, SpyCEP

Question 11

S. pyogenus spreading?

Answer 11

streptokinase (anticoagulant that activates plasminogen into plasmin to degrade fibrin), proteases, lipases and hyaluronidases

Question 12

Necrotising faciitis?

Answer 12

deep infection of skin, destruction of tissue and fascia, development into sever systemic disease w high mortality

Question 13

Diagnosing?

Answer 13

swab purulent material, blood culture for hospitalised patients; gram positive undergo catalase test (Staph + strep -ve) if positive then bacitracin susceptibility (s. pyogenes suscpetible

Question 14

Penicillin function?

Answer 14

binds transpeptidase enzyme, prevents formation of peptide cross-links in bacterial cell wall between 2 sugars, resulting in weak cell wall & cell lysis

Question 15

Beta-lactim antibiotics?

Answer 15

penicillins, cephalosporins, carbapenems

Question 16

S. Pyogenes evasion of immune system?

Answer 16

M protein (binds factor H, prevents C3b opsonisation), toxin secretion and hyaluronic acid capsule