L18 - Infections of the Skin, Soft Tissues, Bones & Joints

Question 1

Define colonisation

Answer 1

The presence of bacteria on the skin, a mucous membrane or a wound without any symptoms or signs of infection

Question 2

Describe the microbiology of normal skin - permanent residents

Answer 2

Staphylococci
Corynebacteria (diptheroids)
Propionibacteria (acne)
Acinetobacter

Question 3

What bacterium can be described as a temporary resident on normal skin?

Answer 3

S. aureus

Question 4

What comprises the transient flora of skin?

Answer 4

Coliforms

Pseudomonas

Question 5

What effect does damaged skin have on colonisation?

Answer 5

Makes skin prone to colonisation with more pathogenic bacteria

Question 6

Give three examples of pathogenic bacteria that colonise damaged skin

Answer 6

S. aureus
Streptococci
Pseudomonas

Question 7

What must happen for colonisation to become infection?

Answer 7

Breaching of the normal skin barrier

Question 8

What are the two main pathogens of skin/soft tissue?

Answer 8

Staph. aureus

Strep. pyogenes

Question 9

Give examples of pathogens affecting the skin/soft tissue - Bacterial

Answer 9

Haemolytic streptococci
Pseudomonas
Coliforms
Anaerobes

Question 10

Give examples of pathogens affecting the skin/soft tissue - Viral

Answer 10

Herpes (HSV, VZV)

Question 11

Give examples of pathogens affecting the skin/soft tissue - Fungal

Answer 11

Dermatophytosis (Tinea)

Question 12

Describe the skin/soft tissue infections caused by S. aureus

Answer 12

Pustular lesions
Impetigo
Cellulitis
Infected wounds
Cannula infections
Toxin-mediated (scalded skin syndrome)

Question 13

Describe the skin/soft tissue infections caused by S. pyogenes

Answer 13

Impetigo
Erysipelas
Cellulitis
Necrotising fasciitis
Toxin-mediated (scarlet fever)

Question 14

Describe a carbuncle

Answer 14

A cluster of boils draining pus onto the skin

Question 15

How are carbuncles treated?

Answer 15

Draining of pus and antibiotic therapy

Question 16

Describe cellulitis

Answer 16

Infection of the upper layers of skin
Erythrema, swelling, painful
Often turns white on pressure
Can cause blisters/ulcers

Question 17

Describe erysipelas

Answer 17

Infection of the upper skin and lymphatics that causes a skin rash on the face/limbs

Question 18

How is erysipelas different from cellulitis?

Answer 18

More superficial

More raised/demarcated

Question 19

Describe impetigo

Answer 19

Yellow, crusting lesions present on the skin
Often heals w/o scarring
Often a mix of S. aureus/S. pyogenes
Very contagious

Question 20

Describe scalded skin syndrome

Answer 20

Due to S. aureus infection (often at distant site) releasing scalded skin syndrome toxin
Layers of skin split, can slough off easily

Question 21

Describe Herpes Simplex - Whitlow

Answer 21

An abscess in the soft tissue near fingernails/toenails

V. painful

Question 22

Describe Shingles (VZV)

Answer 22

Reactivation of dormant Varicella Zozter Virus

Characterised by painful skin rash w/ blisters in a localised area

Question 23

Describe Thrush

Answer 23

Infection w/ Candida

Itching, burning, white discharge

Question 24

Describe Tinea Pedis (Dermatophyte)

Answer 24

Athletes Foot

Fungal infection causing itching, redness and scaling

Question 25

Describe Anthrax

Answer 25

Infection caused by bacillus anthracis Skin form presents as a small blister w/ surrounding swelling that develops into an ulcer w/ black centre Relatively painless

Question 26

Describe necrotising fasciitis

Answer 26

Infection resulting in soft tissue death Sudden onset and rapid spread Red/purple skin, fever, vomiting SEVERE PAIN

Question 27

What is the surgical treatment for necrotising fasciitis?

Answer 27

Debridement, cutting away of soft tissue

Question 28

Describe a central line infection

Answer 28

Infection of inserted central line Can give rise to soft tissue infection Can be v. serious

Question 29

What is the antibiotic therapy for S. aureus?

Answer 29

Flucloxacillin | Co-amoxiclav

Question 30

Define MRSA

Answer 30

Methicillin Resistant Staph Aureus

Question 31

What is the antibiotic therapy for S. pyogenes?

Answer 31

Penicillins | Flucloxacillin

Question 32

What antibiotics are available for treating MRSA/resistant S. pyogenes?

Answer 32

Erythromycin Clindamycin Cefuroxime Vancomycin

Question 33

By what mechanism does resistance arise in MRSA?

Answer 33

PBP2 is the main target site for penicillins in S. aureus MRSA has a mutated PBP2a Cross-resistant to all Beta-lactams Usually resistant to macrolides

Question 34

What proportion of hospital-acquired skin/soft tissue infections are caused by MRSA?

Answer 34

1-2%

Question 35

Define disinfectant

Answer 35

Chemical w/ ability to destroy or inactivate potentially pathogenic micro-organisms

Question 36

Define antiseptic

Answer 36

Disinfectant that can be applied to skin or mucous membranes

Question 37

Define topical antibiotic

Answer 37

Natural/synthetic drug w/ antimicrobial activity applied directly to the skin

Question 38

What are the advantages of topical antibiotics?

Answer 38

High conc at site of infection Can use agents too toxic for systemic use Cheap Combination preparations w/ steroids available

Question 39

What are the disadvantages of topical antibiotics?

Answer 39

May not penetrate to site of infection Can get systemic absorption Resistance

Question 40

Where are topical antibiotics most commonly used?

Answer 40

``` Skin Mucous membranes Mouth Eyes Nose Skin Vagina ```

Question 41

What topical antibiotics are used around the mouth? - What are they treating?

Answer 41

Nystatin (candida)

Question 42

What topical antibiotics are used around the eyes? - What are they treating?

Answer 42

Chloramphenicol/Tetracycline (conjunctivitis)

Question 43

What topical antibiotics are used around the nose? - What are they treating?

Answer 43

Mupirocin (S. aureus/MRSA)

Question 44

What topical antibiotics are used on the skin? - What are they treating?

Answer 44

Fucidin (impetigo) Aciclovir (cold sores) Azoles (fungal infections)

Question 45

Describe septic arthritis

Answer 45

Acute bacterial infection of a joint, often metastatic

Question 46

What are the principle pathogens for SA?

Answer 46

S. aureus S. pyogenes Pneumococcus

Question 47

What are the clinical features of SA?

Answer 47

``` Pain, inflammation Joint effusion Restricted movement Pyrexia Systemic sepsis ```

Question 48

How is SA diagnosed?

Answer 48

Mc&C on Joint aspirate | Blood culture

Question 49

What is the treatment for Septic Arthritis?

Answer 49

High dose of i.v. antibiotics >2wks | Followed by 4wks oral antibiotics

Question 50

Define osteomyelitis

Answer 50

Acute/chronic infection of bone, usually metastatic spread

Question 51

What are the principle pathogens for osteomyelitis?

Answer 51

S. aureus Streptococci M. tuberculosis

Question 52

What are the clinical features of osteomyelitis?

Answer 52

Pain, swelling, fever Systemic sepssis Deformity, collapse (vertebra), fracture

Question 53

How is osteomyelitis diagnosed?

Answer 53

X-ray, bone scan, MRI Blood cultures Bone biopsy

Question 54

What is the treatment for osteomyelitis - Acute

Answer 54

High dose i.v. antibiotics >6wks | +/- surgical drainage

Question 55

What is the treatment for osteomyelitis - Chronic

Answer 55

Formation of sequestrum (dead bone w/i tissue) Months of antibiotics + surgery Often relapses