Bacterial skin infection

Question 1

What are some skin infections that require patients to isolate?

Answer 1

GAS
MRSA
Scabies

Question 2

How can skin infections be spread?

Answer 2

Patients with exfoliative skin conditions shed huge numbers of skin scales and associated bacteria into the environment

Gram +ve bacteria can survive in the environment because of their cell wall structure

These may then become a source of infection for other patients

Question 3

What diagnostic test can be performed on infection of broken skin?

Answer 3

Swabbing and culturing of the lesion

Question 4

What diagnostic test can be performed on deep infective lesions?

Answer 4

Pus or tissue samples

Question 5

What are some examples of bacterial skin infective agents?

Answer 5

• Staphylococcus aureus
• Streptococcus pyogenes (GAS)
• Polymicrobial infection

Question 6

Describe the features of staphylococcus?

Answer 6

Staphylococcus are gram positive cocci that form clusters

They are aerobic and facultatively anaerobic, meaning they grow best in air, but can grow anaerobically

Question 7

What are some toxins produced by staphylococcus aureus?

Answer 7

• Staphylococcal scalded skin syndrome toxin
• Panton Valentine Leukocidin
• Enterotoxin (Food poisoning)
• Toxic Shock Syndrome Toxin (TSST-1)

Question 8

What is the antibiotic of choice in methicillin sensitive S.aureus?

Answer 8

Flucloxacillin

Question 9

What are some antibiotics used in MRSA?

Answer 9

doxycycline PO, co-trimoxazole PO, clindamycin and linezolid

Question 10

What are some skin infections associated with staphylococcus aureus?

Answer 10

• Boils
• Carbuncles
• Cellulitis
• Infected eczema
• Wound infection
• Staphylococcal scalded skin syndrome
• Impetigo
• Infected hair follicles

Question 11

What are some virulence factors associated with S.aureus?

Answer 11

• Capsule
• Fibrinogen binding protein
• Haemolysins
• Coagulase
• Hyaluronidase
• Protein A
• Epidermolytic toxins A/B

Question 12

Is S.aureus coagulase negative or positive?

Answer 12

Positive

Question 13

What are some examples of coagulase negative staphylococci?

Answer 13

Staphylococcus epidermidis
Staphylococcus saprophyticus

Question 14

What are some infections caused by coagulase negative staphylococci?

Answer 14

They are usually skin commensals
UTIs
Artificial material infection

Question 15

Name the infection

Answer 15

Infected eczema

Question 16

Name the infection

Answer 16

Impetigo - Infection in the stratum corneum

Question 17

What causes toxic shock syndrome?

Answer 17

S.aureus producing TSST-1 toxins

Question 18

How does toxic shock syndrome occur?

Answer 18

TSST1 acts as a super-antigen, activating MHCII complexes and resulting in the massive release of cytokines and activating an immune response

Question 19

What are the diagnostic criteria for toxic shock syndrome?

Answer 19

• Fever (>39ºC)
• Diffuse macular rash and desquamation (Diffuse macular erythroderma = Sunburn)
• Hypotension (≤90mmHg)
• ≥3 organ systems involves

Question 20

What are some symptoms of toxic shock syndrome?

Answer 20

High fever, vomiting, diarrhoea, sore throat and muscle pain

Question 21

How does menstrual toxic shock syndrome occur?

Answer 21

Menstrual toxic shock syndrome is a common cause of TSS in which TSST-1 toxins, from S.aureus in a tampon, pass through the perineum and into the blood stream

Question 22

What causes staphylococcal scalded skin syndrome?

Answer 22

Release of SSSST toxin from S.aureus

Question 23

What is the main symptom of staphylococcal scalded skin syndrome?

Answer 23

Separation and lifting of the skin

Question 24

Name the condition

Answer 24

Staphylococcus scalded skin syndrome

Question 25

What is necrotising fasciitis?

Answer 25

This is a bacterial infection spreading alon the fascial planes below the skin surface

Question 26

What occurs as a result of necrotising fasciitis?

Answer 26

This results in rapid tissue destruction beneath the skin, while the surface may not look too abnormal, meaning there will be disproprotionate pain to the skin presentation

Question 27

What are the 2 main types of necrotising fasciitis?

Answer 27

- Type I - Mixed anaerobes and coliforms (Usually post abdominal surgery - Type II - Group A strep infection

Question 28

How can necrotising fasciitis be diagnosed?

Answer 28

Crepitus beneath the skin surface and space on x-ray or CT will show necrotising fasciitis

Question 29

What are some organisms worth treating in leg ulcers?

Answer 29

- Streptococcus pyogenes - Staphylococcus aureus - Other ß-haemolytic streptococci - Anaerobes in diabetic patients - Gram-negatives

Question 30

What is necrotising pneumonia?

Answer 30

This is a preceding influenza-like syndrome with a rapid progression This results in acute respiratory distress, deterioration of pulmonary function, refractory hypoxaemia and multi-organ failure (Despite antibiotic therapy)

Question 31

What are virulence factors?

Answer 31

Virulence factors are factors responsible for pathology and variation in virulence within and between groups of pathogens

Question 32

What are some types of virulence factors?

Answer 32

- Adhesin - Invasin - Impedin - Aggressin - Modulin

Question 33

What is the function of adhesins?

Answer 33

Enables binding of the organism to the host

Question 34

What is the function of invasins

Answer 34

Enables the organism to invade the host cell

Question 35

What is the function of impedins?

Answer 35

Enables the organism to avoid defence mechanisms

Question 36

What is the function of aggressins?

Answer 36

Causes damage to the host directly

Question 37

What is the function of modulins?

Answer 37

Induces damage to the host indirectly

Question 38

Describe the features of streptococci?

Answer 38

Streptococci are gram positive cocci in chains They are aerobic and facultatively anaerobic

Question 39

How are streptococci classified?

Answer 39

Based on haemolysis on blood agar

Question 40

What are the 3 classes of streptococcus?

Answer 40

Alpha haemolytic Beta haemolytic Gamma haemolytic

Question 41

What is meant by alpha haemolysis?

Answer 41

Partial haemolysis of blood agar

Question 42

What is meant by beta haemolysis?

Answer 42

Complete haemolysis of blood agar

Question 43

What is meant by gamma haemolysis?

Answer 43

No haemolysis

Question 44

What colour will alpha haemolysis show on blood agar?

Answer 44

Green tinge

Question 45

What colour will beta haemolysis show on blood agar?

Answer 45

Yellow/Clear

Question 46

What colour will gamma haemolysis show on blood agar?

Answer 46

Red

Question 47

How are the groups of streptococcus classified?

Answer 47

By antigenic surface structures

Question 48

What are some examples of infections caused by group A streptococcus (S.pyogenes)?

Answer 48

- Infected eczema - Impetigo - Cellulitis - Erysipelas - Necrotising fasciitis

Question 49

What skin infection is shown?

Answer 49

Erysipelas

Question 50

What is a toxin produced by GAS?

Answer 50

Streptococcus pyogenes can produce SPE toxins, which act as super antigens and which damage blood vessels This results in Scarlet fever

Question 51

What are the 20 major serotypes of streptococcus?

Answer 51

A-H and K-V

Question 52

How can streptococci be minority classified?

Answer 52

By M-protein antigens

Question 53

What M-protein antigen subtypes are major sub-types?

Answer 53

M1 and M3

Question 54

What M-protein antigen subtypes are serve invasive diseases

Answer 54

M3 and M18

Question 55

What are some common commensal bacteria?

Answer 55

- Staphylococcus epidermidis - Corynebacterium sp. - Proprionibacterium sp.

Question 56

How is necrotising fasciitis usually managed?

Answer 56

Surgical debridement

Question 57

How will Lyme's disease present on the skin?

Answer 57

Target rash

Question 58

What causes Lyme's disease?

Answer 58

Infected tick bite with borellia burgdorferi