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Dermatology > Skin Microbiology; Bacterial & Fungal; Skin infections > Flashcards

Skin Microbiology; Bacterial & Fungal; Skin infections Flashcards

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Dermatology Board Prep flashcards
1
Q

What does the skin DO that provides a good barrier?

A

Constant shedding of the skin

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2
Q

Can bacteria use shed skin?

A

Yes, as a mode of spreading themselves more widely.

Seen in healthcare settings where people are in very close contact with each other.

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3
Q

Pathogenesis of bacteria and humans

A
  1. contact (entry) host
  2. Adhere/colonise and invade
  3. Multiply and complete life cycle
  4. EXIT host

Host is damaged in this process.

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4
Q

Bacterial virulence

A

The capacity of a microbe to cause damage to the host

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5
Q

Virulence factors

A 
> Adhesins 
> Invasin 
> Impedin
> Aggressin
> Modulin
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6
Q

Adhesins

A

Enable binding of the organism to host tissue.

Extra cellular matrix molecules are present on epithelial, endothelial surfaces as well as a component of blood clots.

Fibrinogen-binding (ClfA ClfB)

Collagen binding (CNA)

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7
Q

Invasin

A

Enables the organism to invade host cell/tissue

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8
Q

Impedin

A

Enables the organism to avoid host defence mechanisms

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9
Q

Aggressin

A

Causes damage to host directly

The “car crash” bacteria

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10
Q

Modulin

A

Induces damage to the host indirectly

Chronic infections

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11
Q

Leukocidin

A

killing leukocytes

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12
Q

Staph aureus

where found on body
(types of infections)

A

Anterior nares and perineum

Nosocomial and community infection

Nasal strain can protect

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13
Q

S epidermidis

A

100% colonisation
skin & mucous membranes

nosocomial infection/immunocompromised
- catheters

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14
Q

MRSA

A

Nosocomial

Elderly and immunocompromised 
Intensive care units
Burns patients 
Surgical patients 
IV lines
Dialysis patients
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15
Q

Staph aureus has a range of infections. It is very flexible.

Due to…

A

VERY STRONG VIRULENCE FACTORS

Superficial lesions
- boils to abscesses

Systemic
- life threatening

Toxinoses

  • toxic shock
  • scalded skin syndrome
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16
Q

Evasion of host defences

A 
CAPSULE
Protein A
Superantigens 
Coagulase
Gamma toxin 
Alpha toxin 
PVL cytotoxin
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17
Q

2 types of capsule

A

Mucoid

Microcapsule

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18
Q

Toxinoses

A

> TSST-1
- rapid progression high fever, d&v, sore throat, muscle pain

> SSS (scalded skin syndrome)

    • exfoliation toxins, often neonatal, face, axillae and groin
    • ETA & ETB toxins target desmoglein 1 (DG-1)
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19
Q

What toxins (from S.aureus) bring about SSS?

A

ETA & ETB toxins

They target desmoglein 1. (integrity of desmosomes)

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20
Q

Superantigens

A

Activate 1 in 5 t cells. (normally 1 in 10000)

TSST-1 in particular associated with toxic shock

MASSIVE release of cytokines and inappropriate immune response.

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21
Q

What is TSST>

A

Toxic Shock Syndrome Toxin

Causes toxic shock.

Staph aureus infection.

Toxins absorbed through vaginal walls.

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22
Q

Toxic Shock syndrome - diagnostic criteria

A

> Fever - 39°C
Diffuse macular erythrodema

> Hypotension (≤90mmHg)

> ≥3 organs systems involved

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23
Q

PVL (Panton Valentine Leukocidin)

A

Specific toxicity for leukocytes.

Severe skin infections.

e. g. recurrent furunculosis
- sepsis/ necrotising fasciitis

PVL & alpha toxin - linked with CA-MRSA responsible for necrotising pneumonia and contagious severe skin infections.

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24
Q

Necrotising pneumonia

A

> Preceding influenza link syndrome

> Necrotising haemorrhagic pneumonia

> RAPID PROGRESSION

> Acute respiratory distress

> Deterioration in pulmonary function

> Refractory hyperaemia

> Multi-organ failure despite Abx therapy

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25
Q

Strep pyogenes

A 
Gram +ve cocci
Chains
Catalase NEGATIVE
Haemolysis
- Beta haemolytic

Surface antigen

Skin infections

  • impetigo
  • cellulitis
  • necrotising fasciitis
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26
Q

Some infections caused by Strep pyogenes

A

Impetigo
Cellulitis
Necrotising fasciitis

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27
Q

Lancefield system

A

> Serotyping of cell wall carbohydrate
Groups A-H & K-V

Group A further subdivided according to M protein antigens.

  • M1 and m3 major serotype
  • M3 & M18 severe invasive
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28
Q

Adhesion

A

Oropharynx and nasopharynx

Non ciliated cells covered in mucous

Hyaluronic Acid (capsule)
- CD44 +ve keratinocytes

We have hyaluronic acid n our bodies - so the body has difficulty recognising the foreign pathogen.

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29
Q

Hyaluronic acid capsule

A

Similar to human hyaluronic acid

Mucoid colonies produced by high levels of capsule production

Produced in early exponential growth

Reduces phagocytosis

Highly encapsulated & M rich GAS are virulent

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30
Q

More encapsulated =

A

more virulent

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31
Q

Impetigo

A

Group A strep skin disease

Highly contagious through contact with discharge on the face.

Infection immediately below surface (stratum corneum)

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32
Q

What does GAS stand for?

A

Group A Streptococcal

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33
Q

Cellulitis

A

Group A strep infection

Deeper skin infection in the dermis

Not associated with necrosis

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34
Q

Cellulitis is not associated with…

A

necrosis

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35
Q

Erysipelas

A

Fever
Rigours
Nauseas

GAS

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36
Q

Necrotising fasciitis (type ii)

A

Invasive Strep A strains penetrate mucous membrane and develop in lesion.

Rapidly destroys connective tissue.

AMPUTATION TERRITORY

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37
Q

Streptolysins

A

Pore forming cytolysin

Toxic to PMN (neutrophils), organelles, platelets

38
Q

Toxic Shock LIKE syndrome (TSLS)

A

S. pyogenes

Pyrogenic exotoxin (produces fever)

Complication of invasive infection

30% mortality

Hours to days

Hypotension to organ failure

SpeB and SpeC (superantigens)

39
Q

Toxic Shock - S. aureus and S pyogenes

A 
S. aureus
localised infection
no bacteremia
Menstrual TSST-1
Non-menstural SEB or  SEC
pyrogenic toxin

Virulence Factor
Superantigen

S. pyogenes
invasive disease (pharyngitis)
SpeA & SpeC most common toxin

pyrogenic toxin

Virulence factor
Superantigen

40
Q

Where is S. pyogenes normally found?

A

Pharynx

41
Q

Variation of virulence factors caused by…

A

Variation in genes

42
Q

Defence against infection

A

Less likely to become infected if skin is intact

dry - desiccation of microorganisms

Sebum - fatty acids (inhibit bacterial growth)

Competitive bacterial flora

Concept of resident and transient flora

43
Q

Competitive bacterial flora

A

Staph. epidermis

Corynebacterium sp. (diphtheroids)

Propionibacterium sp.

44
Q

Medical name for a boil

A

Furuncle

45
Q

When would you swab an ulcer/boi; etc

A

If lesion surface is broken/looks infected

Pus or tissue if deeper lesion

46
Q

Is Staph aureus coagulase negative or positive?

A

Positive.

All other staph are coagulase negative.

47
Q

Which species of Staphylococcus is Novobiocin resistant?

A

S. saprophyticus

All other staph are SENSITIVE

48
Q

Staph species

A

Gram positive cocci in clusters

Aerobic and facultatively anaerobic

49
Q

S. aureus

A

Clots plasma

Causes wound, skin, bone and joint infections

Enterotoxin - food poisoning
SSSST
PVL

50
Q

Treatment for a staph aureus infection?

A

FLUCLOX
FLUCLOX
FLUCLOX

51
Q

SSSST

A

Staphylococcal scalded skin syndrome toxin

52
Q

If resistant to methicillin…it will be resistant to

A

Fluclox

53
Q

Carbuncle

A

red, swollen, and painful cluster of boils that are connected to each other under the skin.

54
Q

Staph aureus - skin infections

A

> Boils and carbuncles

> Minor skin sepsis

> Cellulitis

> Infected eczema

> Impetigo

> Wound infection

> Staphylococcal SSS

55
Q

Classic sign of Impetigo

A

Golden crusting of lesions

56
Q

MRSA treatmetn

A

Doxycycline
Co-trimoxazole
Clindamycin
Vancomycin

57
Q

Coagulase negative Staphs (Staph epidermidis)

A

> Skin commensals (not usually pathogenic)

> Infection in association with implanted artificial material (heart valves, joints, IV catheters)

58
Q

What can Staph. saprophyticus cause?

A

Urinary tract infection in women of child-bearing age.

59
Q

Strep species

A

Gram positive and in chains (strips)

Aerobic and facultatively anaerobic

Classified initially by haemolytic on blood agar

  • Beta (complete)
  • alpha (partial)
  • gamma (none)

Further classified by antigenic structure on surface

  • Group A
  • Group B
60
Q

If bacteria appears as a “chain” and is beta haemolytic… what is it?

A

Group A Strep (GAS)

61
Q

Beta-haemolytic Strep

A

> Pathogenic
Haemolysin is one of many toxins

> Further classified by antigenic structure on surface

  • Group A
  • Group B
62
Q

Group A strep

A

Throat

Severe skin infections

63
Q

Group B strep

A

Meningitis in neonates

64
Q

Important categories of alpha haemolytic strep

A

> Strep pneumoniae - pathogen, commonest, cause of pneumonia

> Strep viridian’s group - commensals of mouth, throat, vagina - cause infection, endocarditis

65
Q

Non-haemolytic Streptococci

A

Enteroccus species (E. faecalis, E calcium)

Commensals of bowel

Common causes of UTI

66
Q

Scalded Skin syndrome

A

Caused by staphylococcal infection

Shearing/sloughing/peeling of skin

Seen in children/new borns

Sometimes seen in drug users

67
Q

Strep pyogenes

A

GAS

Infected eczema
Impetigo
Cellulitis
Erysipelas (superficial form of cellulitis)
Necrotising fasciitis
68
Q

Crepitus of muscles can be caused by?

A

Necrotising fasciitis

69
Q

Strep pyogenes treatment

A

Penicillin

flucloxacillin too

70
Q

Necrotising fasciitis treatment

A

Immediate surgical debridement as well as Abx

71
Q

Necrotising fasciitis

2 types.

A

Bacterial infection spreading along fascial planes below skin surface –> rapid tissue destruction.

SEVERE PAIN. Little skin signs.

2 types
- I: mixed anaerobes and coliform, usually post abdo surgery

  • II: Group A strep Infection

Urgent surgical opinion and debridement required

Abx treatment depends on organisms

72
Q

Fournier gangrene

A

Gangrene affecting the perineum

More likely in diabetics

73
Q

Tinea means…

A

Ringworm. Not a worm, but raised outer borders of lesions in an annular pattern looks like a ringworm.

Tinea capitals - scalp
" barbae - beard
" corporis - body
" manuum - hand
" unguium - nails
" cruris - groin
" pedis - foot

DERMATOPHYTE

74
Q

Dermatophyte pathogenesis

A

Fungus enters abraded or soggy skin
Hyphae spread in stratum corneum
Infects keratinised tissues only (skin, hair, nails)
Increased epidermal turnover causes scaling
Inflammatory response provoked (dermis)
Hair follicles and shafts invaded
Lesion grows outward and heals in centre, giving a “ring” appearance

75
Q

Who is more commonly affected by dermatophyte infections?

A

Men

mainly foot and groin

76
Q

Scalp ringworm normally affects…

A

Children

77
Q

Sources of dermatophyte infection

A
  • other infected humans*
  • antrhopophilic fungi

Animals (cats, dogs, cattle)
- zoophilic fungi

Soil (less common UK)
- geophilic fungi

78
Q

Dermatophytes - causal organisms

A

**Trichophyton rubrum (human-human) **

Trichophyton mentagraphytes (next most common, human-human)

Microsporum canis
- cats, dogs, humans

79
Q

Main cause of dermatophyte infection?

A

TRICHOPHYTON RUBRUM

80
Q

Dermatophyte infection - diagnosis

A

Clinical appearance

Woods light (fluorescence)

Skin scrapings, nail clippings, hair

  • send to lab in a dermapak
  • culture takes 2 weeks+
81
Q

When sending samples of suspected dermatophytes, what do you send them in?

A

Dermapaks.

82
Q

Dermatophyte infection - treatment

A

> Small areas of infected skin, nails = Clotrimazole cream or similar
, topical nail paint

> Extensive skin infections
> nail infections
> Scalp infections
- terbinafine orally
- itraconazole orally
83
Q

Candida skin infection

A

causes infection in skin folds where area is warm and moist (candida intertrigo)

Seen under breasts in females, groin areas, abdo skin folds, nappy area in babies

SWAB for culture

84
Q

Candida - treatment

A

Clotrimazole cream

Oral fluconazole

85
Q

Scabies

A

Sarcoptes scabiei

6 weeks’ incubation

Intensely itchy rash affecting finger webs, wrists, genital area

86
Q

Chronic crusted form of scabies =

A

Norwegian scabies

87
Q

Scabies - treatment

A

Malathion lotion (applied to whole body, washed off next day)

Benzyl benzoate (avoid in children)

88
Q

What treatment should be avoided in children with scabies?

A

Benzyl benzoate

89
Q

Lice infestation (pediculosis)

A

INTENSE ITCH

Pediculis wapitis (head louse)

Pediculus corporis (body louse)

Phthirus pubis (pubic louse)

Malathion for treatment

90
Q

Lice - treatment

A

Malathion

91
Q

Infection control - dermatology

A

Exfoliative skin conditions are an issue.

Gram pos bacteria can survive in the environment because of their cell wall

Source of infection for other patients

SO

Gloves and plastic aprons (contact precautions)

Single room isolation for some patients

  • GAS infection
  • MRSA infection
  • Scabies (long sleeved gowns required)

Dermatology (8 decks)

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