Chapter 18

Question 1

Where are normal skin flora number higher?

Answer 1

In moist areas

Question 2

How does shedding protect from viral skin infections?

Answer 2

Viruses cannot replicate in dead cells

Question 3

What are the routes of skin infections?

Answer 3

Break of intact skin (infection from outside)
Skin manifestations of systemic infections
Toxin mediated skin damage (toxin in blood to skin)

Question 4

What is staphylococcus aureus?

Answer 4

The most common skin pathogen, “swiss army knife” has virulence factors to counter almost every defence mechanism we have

Question 5

What do staphylococcal skin infections cause?

Answer 5

Boils, abscesses to scaled skin syndrome, Toxic shock syndrome

Question 6

What is the resistant form of staph aureus?

Answer 6

Methicillin resistant staph aureus

Question 7

What is a boil?

Answer 7

A superficial infection of the hair follicle (folliculitis)

Question 8

How does a boil progress?

Answer 8

Infection of the hair follicle multiplies and locally spread to cause an inflammatory reaction and an influx of neutrophils (pus), may drain inward and spread the bacteria

Question 9

How is a boil treated?

Answer 9

Daring, antibiotics for severe infections (with fever)

Question 10

Who will have recurrent infections of staphylococcus skin infections?

Answer 10

Nasal carriers will have recurrent infection

Question 11

What happens in scalded skin syndrome?

Answer 11

The exfoliation toxin destroys the intercellular connections of the skin causing separation of the epidermis and large blisters

Question 12

How is scalded skin syndrome treated?

Answer 12

Fluid replacement and antibiotics

Question 13

What is Toxic Shock Syndrome?

Answer 13

Systemic infections from staph aureus that affect multiple organ systems

Question 14

What are the symptoms of TSS?

Answer 14

Fever, hypotension, diffused red rashes and desquamation of the skin (limited to palms and soles of feet)

Question 15

Why do tampons cause TSS?

Answer 15

The synthetic absorbent material holds lots of blood, which is the growth media for staph aureus (vaginal microflora) and produces toxins

Question 16

What is the cause behind many streptococcal skin infections?

Answer 16

S. pyogenes

Group A streptococci

Question 17

What are some streptococcal skin infections?

Answer 17

Impetigo and erysipelas, cellulitis, necrotizing fasciitis

Question 18

How does impetigo occur?

Answer 18

Strep is acquired through contact with infected skin lesions and then it invades minor breaks in the skin, causing lesions. Deeper=lesions

Question 19

What is erysipelas?

Answer 19

An acute deeper infection of the dermis by strep. Can lead to bacteremia. Red rosy rash on face

Question 20

What does the virulence of GAS depend on?

Answer 20

Climate, humidity, race, trauma

Question 21

How is the s. pyogenes that infects the skin different from the one that infects the throat?

Answer 21

Subdivision of the species based on surface proteins (M proteins attached to PG)

Question 22

What is the incubation time for S. pyogenes skin infections?

Answer 22

24-48 hours post skin invasion

Question 23

What are the virulence factors of S. pyogenes?

Answer 23

Hyaluronidase and toxic products to facilitate its spread through the tissue

Question 24

What is the lysogenized strain of S. pyogenes? What does it do?

Answer 24

A strain that has been lysogenized by macrophages and now produces pyrogenic endotoxin causing a red rash

Question 25

What may S. pyogenes of the skin cause?

Answer 25

A toxic shock like syndrome

Question 26

What is cellulitis?

Answer 26

A diffuse inflammation and infection of the skin, deeper than erysipelas and originates from a superficial infection or following trauma May have systemic features

Question 27

What are the systemic features that may occur with cellulitis?

Answer 27

Fever, malaise, headache, elevated white blood cell count

Question 28

How is cellulitis treated?

Answer 28

Use empirical antibiotic treatment until cause is known (most likely Gram + cocci)

Question 29

What causes cellulitis usually?

Answer 29

S. pyogenes, GAS

Question 30

What is necrotizing fasciitis?

Answer 30

A 'flesh-eating disease' | Acute, highly toxic infection with a high mortality rate resulting from trauma to the skin

Question 31

What causes necrotizing fasciitis?

Answer 31

Often polymicrobial | Anaerobes, facultative anaerobes like S. pyogenes (don't need oxygen)

Question 32

How do facultative anaerobes cause blisters?

Answer 32

They produce gas

Question 33

What causes gas gangrene?

Answer 33

``` Clostridial sp (C. perfringens) Anaerobes ```

Question 34

How does C. perfringens work?

Answer 34

``` Contamination with spores Produces lecithinase (like snake venom) which precipitates protein ```

Question 35

What are the clinical manifestations of gas gangrene?

Answer 35

Severe pain, edema, cellulitis, production of gas and foul-smelling purulent discharge

Question 36

How is gas gangrene treated?

Answer 36

Amputation, hyperbaric chamber (saturates with O2 to kill anaerobes) and antibiotics

Question 37

How can we tell if a pathogen is producing lecithinase?

Answer 37

Put sample on egg white media, put in antibodies against lecithinase which will bind and inactivate, stopping it's precipitation of proteins.