Skin Microbial Interactions and Wound Healing

Question 1

When do skin microbial diseases arise?

Answer 1

Opportunity (e.g. wound)

Population imbalance

Question 2

What prevents bacterial penetration to the dermis?

Answer 2

Keratinisation

Question 3

Within the dermis, where is the site of bacterial colonisation?

Answer 3

Sweat glands

Question 4

What does gland secretions contain?

Answer 4

Slightly acidic sweat from the sebaceous glands

Anti-microbial peptides

Question 5

Which layer of bacterial penetration causes illness?

Answer 5

Hypodermis

Question 6

Give an example of a disease associated with hypodermal bacterial entry

Answer 6

Necrotizing fasciitis

Question 7

What causes necrotizing fasciitis?

Answer 7

bacteria from soil enters the skin through through a deep wound and colonises in the hypodermis

Question 8

What are the immune defences in the epidermis?

Answer 8

Langerhan cells
Keratinocytes
CD8+ T cells

Question 9

What is the function of keratinocytes in association with immune defence?

Answer 9

• Possess Toll like receptors
• Detect pathogen
• Release cytokines to induce Langerhan’s and T cell movement to site of infection

Question 10

What are the immune defences in the dermis?

Answer 10

Dermal dendritic cells
Macrophages
Innate lymphoid cells (ILC)

Question 11

What is the function of the innate lymphoid cells?

Answer 11

Orchestrate immune responses among T cells and can suppress attack of bacteria

Question 12

What are the three phases of wound healing?

Answer 12

1) Inflammatory phase
2) Proliferative phase
3) Remodeling phase

Question 13

What happens in the inflammatory phase?

Answer 13

Release of inflammatory cytokines to promote chemotaxis

Accumulation of pus

Question 14

What promotes growth?

Answer 14

Mitogenic

Epithelial growth factor (EGF) - growth of fibroblasts and keratinocytes

Question 15

What do fibroblasts do in relation to the inflammatory phase?

Answer 15

Cause scaring through collagen and connective tissue deposition

Question 16

What do keratinocytes do in relation to the inflammatory phase?

Answer 16

Recreate the epidermal layer

Question 17

What is the role of IL-6 in the inflammatory phase?

Answer 17

Induce fever

Question 18

Describe the proliferative phase

Answer 18

• Epithelization
• Angiogenesis in the dermis
• Fibroblast proliferation in the dermis

Question 19

What is epithelialisation?

Answer 19

Growth and division of epithelial cells from the stratum basale

Question 20

What is angiogenesis?

Answer 20

Production of new blood vessels

Question 21

Why is fibroblast proliferation important in the proliferative phase?

Answer 21

Deposit collagen into the dermis which provides a supportive matrix for epidermal keratinocyte growth

Question 22

What do fibroblasts produce?

Answer 22

Dermal granulation tissue

Question 23

What does dermal granulation tissue consist of?

Answer 23

• main signals are PDGF and EGF
• collagen type III
• Glycosaminoglycans
• Fibronectin
• Elastin fibres

Question 24

What induces fibroblasts?

Answer 24

TGF-beta1

Question 25

What happens in the remodeling phase?

Answer 25

- Scaring - Collagen reorganisation - Cross linking of collagen

Question 26

What causes scaring?

Answer 26

The conversion of type III collagen to type I

Question 27

Why is there cross linking of collagen?

Answer 27

Increase tensile strength

Question 28

What local effects affect wound healing?

Answer 28

``` Oedema Ischemia - perfusion of the wound Impaired healing Infection Foreign bodies ```

Question 29

where is beta-defensin secreted from?

Answer 29

All epithelial cells | - in the skin = keratinocytes and sebaceous duct cells

Question 30

What are defensins?

Answer 30

anti-microbial peptides

Question 31

what are defensins involved in?

Answer 31

Innate immune response mechanism

Question 32

How do defensins function?

Answer 32

Permeabilise bacteria outer wall causing lysis

Question 33

Give an example of a 'good' bacteria

Answer 33

Staphylococcus epidermidis

Question 34

Describe the function of staphylococcus epidermidis in terms of prevention of disease

Answer 34

has mechanisms for host immune invasion | resists harmful yeast and bacteria colonisation

Question 35

Give an example of a 'bad' bacteria

Answer 35

Staphylococcus aureus

Question 36

name a pathogen associated with staphylococcus aureus

Answer 36

MRSA

Question 37

how does the staphylococcus aureus function?

Answer 37

will colonise human skin, lung and gut. opportunistic pathogen causes boils and abscesses

Question 38

give 2 examples of what staphylococcus aureus secretes?

Answer 38

Coagulase (blood clots) | Lipase (degrades protective sebaceous oils)

Question 39

What is an infection caused by staphylococcus aureus

Answer 39

folliculitis

Question 40

How does the infection of follicultis arise?

Answer 40

Staphylococcus aureus invades down the shaft of the hair follicle Causes inflammation and infection of the hair follicle and sebaceous gland.

Question 41

What is quorum sensing?

Answer 41

Homeostatic mechanism involving released peptide signals that keep bacterial populations stable

Question 42

what peptide signals do quorum sensing detect?

Answer 42

Autoinducer peptides

Question 43

What happens when there is a low concentration of s. epidermis?

Answer 43

``` Decrease the amount of inducer peptides Causes phosphorylation of the ArgC Activation of ArgA Growth and cell division Increase the concentration of s. epidermis ```

Question 44

What happens if you get a s. aureus infection?

Answer 44

Autoinducer peptides inhibit ArgC resulting in cell death

Question 45

Give an example of a fungal inhabitant of the epidermis

Answer 45

Malassezia - causes dandruff

Question 46

What is malassezia function

Answer 46

Secretion of phospholipase | Cleaves sebum lipids to inflammatory signals (e.g. arachidonic acid)

Question 47

how does malassezia alter skin epithelial function?

Answer 47

Synthesise anti-bacterial compounds from skin amino acids and peptides Modifies keratinocyte sensitivity to UVA damage Inhibits melanin production Inhibits langerhans cell immune signalling

Question 48

Where is acne bacteria found?

Answer 48

dermal pores and hair follicles

Question 49

Where is the acne nutrient source from?

Answer 49

Sebum | Shed keratin

Question 50

where does the acne bacteria proliferate in?

Answer 50

The sebaceous gland

Question 51

how does the pustule head of acne form?

Answer 51

The proliferation in the sebaceous gland causes swelling of the lumen of the gland this lumen filled with bacteria the bacteria moves all the way up through the epidermsi

Question 52

how is sebum produced?

Answer 52

holocrine secretion

Question 53

What prevents acne?

Answer 53

Isotrentoin

Question 54

How does isotrentoin prevent acne?

Answer 54

inhibits sebaceous holocrine secretion

Question 55

Possible cause of acne

Answer 55

genetic condition involving failure of cell polarisation

Question 56

What does isotrentoin release?

Answer 56

13cis retinoic acid

Question 57

Two results of isotrentoin

Answer 57

Sebocyte secretion arrested | Sebocyte re-growth arrested

Question 58

How does sebocyte re-growth arresting cause reduced inflammation?

Answer 58

-> sebaceous gland lumen unblocked -> conditions less favourable for P. Acnes growth -> inflammation subsides