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Dermatology > Bacterial skin infection > Flashcards

Bacterial skin infection Flashcards

1
Q

What are some skin infections that require patients to isolate?

A

GAS
MRSA
Scabies

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2
Q

How can skin infections be spread?

A

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

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3
Q

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

A

Swabbing and culturing of the lesion

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4
Q

What diagnostic test can be performed on deep infective lesions?

A

Pus or tissue samples

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5
Q

What are some examples of bacterial skin infective agents?

A
  • Staphylococcus aureus
  • Streptococcus pyogenes (GAS)
  • Polymicrobial infection
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6
Q

Describe the features of staphylococcus?

A

Staphylococcus are gram positive cocci that form clusters

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

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7
Q

What are some toxins produced by staphylococcus aureus?

A
  • Staphylococcal scalded skin syndrome toxin
  • Panton Valentine Leukocidin
  • Enterotoxin (Food poisoning)
  • Toxic Shock Syndrome Toxin (TSST-1)
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8
Q

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

A

Flucloxacillin

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9
Q

What are some antibiotics used in MRSA?

A

doxycycline PO, co-trimoxazole PO, clindamycin and linezolid

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10
Q

What are some skin infections associated with staphylococcus aureus?

A
  • Boils
  • Carbuncles
  • Cellulitis
  • Infected eczema
  • Wound infection
  • Staphylococcal scalded skin syndrome
  • Impetigo
  • Infected hair follicles
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11
Q

What are some virulence factors associated with S.aureus?

A
  • Capsule
  • Fibrinogen binding protein
  • Haemolysins
  • Coagulase
  • Hyaluronidase
  • Protein A
  • Epidermolytic toxins A/B
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12
Q

Is S.aureus coagulase negative or positive?

A

Positive

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13
Q

What are some examples of coagulase negative staphylococci?

A

Staphylococcus epidermidis
Staphylococcus saprophyticus

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14
Q

What are some infections caused by coagulase negative staphylococci?

A

They are usually skin commensals
UTIs
Artificial material infection

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15
Q

Name the infection

A

Infected eczema

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16
Q

Name the infection

A

Impetigo - Infection in the stratum corneum

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17
Q

What causes toxic shock syndrome?

A

S.aureus producing TSST-1 toxins

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18
Q

How does toxic shock syndrome occur?

A

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

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19
Q

What are the diagnostic criteria for toxic shock syndrome?

A
  • Fever (>39ºC)
  • Diffuse macular rash and desquamation (Diffuse macular erythroderma = Sunburn)
  • Hypotension (≤90mmHg)
  • ≥3 organ systems involves
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20
Q

What are some symptoms of toxic shock syndrome?

A

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

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21
Q

How does menstrual toxic shock syndrome occur?

A

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

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22
Q

What causes staphylococcal scalded skin syndrome?

A

Release of SSSST toxin from S.aureus

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23
Q

What is the main symptom of staphylococcal scalded skin syndrome?

A

Separation and lifting of the skin

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24
Q

Name the condition

A

Staphylococcus scalded skin syndrome

25
Q

What is necrotising fasciitis?

A

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

26
Q

What occurs as a result of necrotising fasciitis?

A

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

27
Q

What are the 2 main types of necrotising fasciitis?

A
  • Type I - Mixed anaerobes and coliforms (Usually post abdominal surgery
  • Type II - Group A strep infection
28
Q

How can necrotising fasciitis be diagnosed?

A

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

29
Q

What are some organisms worth treating in leg ulcers?

A
  • Streptococcus pyogenes
  • Staphylococcus aureus
  • Other ß-haemolytic streptococci
  • Anaerobes in diabetic patients
  • Gram-negatives
30
Q

What is necrotising pneumonia?

A

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)

31
Q

What are virulence factors?

A

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

32
Q

What are some types of virulence factors?

A
  • Adhesin
  • Invasin
  • Impedin
  • Aggressin
  • Modulin
33
Q

What is the function of adhesins?

A

Enables binding of the organism to the host

34
Q

What is the function of invasins

A

Enables the organism to invade the host cell

35
Q

What is the function of impedins?

A

Enables the organism to avoid defence mechanisms

36
Q

What is the function of aggressins?

A

Causes damage to the host directly

37
Q

What is the function of modulins?

A

Induces damage to the host indirectly

38
Q

Describe the features of streptococci?

A

Streptococci are gram positive cocci in chains

They are aerobic and facultatively anaerobic

39
Q

How are streptococci classified?

A

Based on haemolysis on blood agar

40
Q

What are the 3 classes of streptococcus?

A

Alpha haemolytic
Beta haemolytic
Gamma haemolytic

41
Q

What is meant by alpha haemolysis?

A

Partial haemolysis of blood agar

42
Q

What is meant by beta haemolysis?

A

Complete haemolysis of blood agar

43
Q

What is meant by gamma haemolysis?

A

No haemolysis

44
Q

What colour will alpha haemolysis show on blood agar?

A

Green tinge

45
Q

What colour will beta haemolysis show on blood agar?

A

Yellow/Clear

46
Q

What colour will gamma haemolysis show on blood agar?

A

Red

47
Q

How are the groups of streptococcus classified?

A

By antigenic surface structures

48
Q

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

A
  • Infected eczema
  • Impetigo
  • Cellulitis
  • Erysipelas
  • Necrotising fasciitis
49
Q

What skin infection is shown?

A

Erysipelas

50
Q

What is a toxin produced by GAS?

A

Streptococcus pyogenes can produce SPE toxins, which act as super antigens and which damage blood vessels

This results in Scarlet fever

51
Q

What are the 20 major serotypes of streptococcus?

A

A-H and K-V

52
Q

How can streptococci be minority classified?

A

By M-protein antigens

53
Q

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

A

M1 and M3

54
Q

What M-protein antigen subtypes are serve invasive diseases

A

M3 and M18

55
Q

What are some common commensal bacteria?

A
  • Staphylococcus epidermidis
  • Corynebacterium sp.
  • Proprionibacterium sp.
56
Q

How is necrotising fasciitis usually managed?

A

Surgical debridement

57
Q

How will Lyme’s disease present on the skin?

A

Target rash

58
Q

What causes Lyme’s disease?

A

Infected tick bite with borellia burgdorferi

59
Q
A

Dermatology (38 decks)

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