Skin and Soft tissue Infections

Question 1

What bacteria colonise the skin as normal flora?

Answer 1

Coagulase-negative staphylococci,
Staph. aureus,
Propionibacterium,
Corynebacterium spp.

Question 2

Where does Herpes simplex reside in its dormant state and how does a secondary infection present?

Answer 2

Dorsal root ganglions as episomes

When activated it migrates along the sensory nerves to form weeping, vesicular lesions

Question 3

Which virus is usually responsible for cold sores and genital herpes?

Answer 3

Herpes simplex virus (HSV)

Peri-oral = HSV 1
Genital = HSV 2

Question 4

What is the treatment for HSV?

Answer 4

Cold sores: Topical acyclovir

Genital herpes or immunosuppressed patient: Oral acyclovir

Question 5

What causes shingles and what is seen on examination?

Answer 5

Varicella Zoster Virus (VZV) can reactivate to cause Herpes zoster (Shingles)

Weeping, vesicular rash
Dermatomal distribution

Question 6

What is the treatment for herpes zoster?

Answer 6

Oral acicolvir / valaciclovir

IV aciclovir - depending on age of patient, immune status and severity of shingles

Question 7

How does Molluscum contagiosum present clinically?

Answer 7

Raised, pearly lesions up to 3 mm
Umbilicated

No treatment needed - disappear after 6-18 months

Question 8

What exotoxins does S. aureus produce?

Answer 8

Epidermolytic toxins A & B (ETA & ETB),

Toxic shock syndrome toxin (TSST-1),

Panton-Valentine leukocidin (PVL)

Question 9

What is impetigo and its causative organisms?

Answer 9

Infection of epidermis (superficial)

Staph. aureus,
Strep. pyogenes
or both

Question 10

What does impetigo look like upon examination?

Answer 10

Plaque-like lesions
Yellowish exudate
Thick scabs - “Honey crusted lesions”

Question 11

What local and generalised complications of impetigo are caused by Epidermolytic toxin production (ETA & ETB)?

Answer 11

Localised: Bullous impetigo
Generalised: Staphylococcal scalded skin syndrome (SSSS)

Desmosomal glycoprotein desmoglein-1
Required for cell-to-cell adhesion in the superficial epidermis
Inactivated by ETA & ETB

Question 12

What is Erysipelas its suspected causative agent?

Answer 12

Infection of dermis
Predominantly face or shin

Strep. pyogenes

Question 13

What is Cellulitis and its usual causative agent?

Answer 13

Infection of skin and subcutaneous tissues

Staph. aureus
Strep. pyogenes
Pasteurella multocida (animal bites)
Haemophilus influenzae

Question 14

Describe the bacteria that causes Anthrax

Answer 14

Bacillus anthracis

Spore-forming aerobic Gram-positive bacillus

Question 15

How is Bacillus anthracis acquired and how does it present?

Answer 15

Acquired from imported wool, hair and animal hides

Inoculation through breaks in the skin:
a painless ulcer with a black centre (eschar)

Question 16

What causes Type 1 Necrotising fasciitis?

Answer 16

Type 1: Polymicrobial

• Enteric Gram-negative bacilli
• Anaerobes

Question 17

What causes Type 2 Necrotising fasciitis?

Answer 17

Type 2: Streptococcus pyogenes

Question 18

How does necrotising fasciitis present and how is it treated?

Answer 18

Spontaneous or at site of skin penetration, Any part of body

Fever & malaise + Dark, rapidly spreading, necrotic lesion

Treatment: Intravenous antibiotics and Surgical debridement

Question 19

Where do you most commonly find anaerobic infections of the skin?

Answer 19

Gas gangrene
Usually post-operative surgical sites
eg. amputations

Question 20

What organism causes anaerobic infections of the skin?

Answer 20

Clostridium perfringens (anaerobic Gram-positive bacillus)

Causes gas gangrene

Question 21

What is the empiric treatment for Staph. aureus or Strep. pyogenes infections

Answer 21

Flucloxacillin

Question 22

What is the empiric treatment for impetigo?

Answer 22

Fusidic acid or mupirocin

Question 23

What is the empiric treatment for Necrotising fasciitis?

Answer 23

need to cover anaerobes, Enterobacteriaceae, streptococci and staphylococci

Meropenem + clindamycin

Question 24

What is the most like suspect for gas gangrene and how is it treated?

Answer 24

Clostridium perfringens

Intravenous antibiotics
Surgical debridement

Question 25

What is the empiric treatment for MRSA?

Answer 25

Vancomycin

Question 26

What are the causative agents of Dermatophyte infections?

Answer 26

Dermatophyte fungi:
Tricophyton spp. (e.g. T. rubrum)
Microsporum spp. (e.g. M. canis)

Question 27

What is the pathogenesis of dermatophyte infections?

Answer 27

Dermatophytes use keratin as nutritional substrate
Usually restricted to stratum corneum
Rarely penetrate the living cells of the epidermis

Question 28

What is onchomycosis?

Answer 28

Dermatophyte infection of a nail

Question 29

What would you use to treat a fungal skin infection topically?

Answer 29

Clotrimazole

Terbinafine

Question 30

What would you use to treat a fungal scalp and nail infection systemically?

Answer 30

Itraconazole