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

Skin Microbiology; Bacterial & Fungal; Skin infections Flashcards

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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
Strep pyogenes
``` Gram +ve cocci Chains Catalase NEGATIVE Haemolysis - Beta haemolytic ``` Surface antigen Skin infections - impetigo - cellulitis - necrotising fasciitis
26
Some infections caused by Strep pyogenes
Impetigo Cellulitis Necrotising fasciitis
27
Lancefield system
> 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
28
Adhesion
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.
29
Hyaluronic acid capsule
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
30
More encapsulated =
more virulent
31
Impetigo
Group A strep skin disease Highly contagious through contact with discharge on the face. Infection immediately below surface (stratum corneum)
32
What does GAS stand for?
Group A Streptococcal
33
Cellulitis
Group A strep infection Deeper skin infection in the dermis Not associated with necrosis
34
Cellulitis is not associated with...
necrosis
35
Erysipelas
Fever Rigours Nauseas GAS
36
Necrotising fasciitis (type ii)
Invasive Strep A strains penetrate mucous membrane and develop in lesion. Rapidly destroys connective tissue. AMPUTATION TERRITORY
37
Streptolysins
Pore forming cytolysin Toxic to PMN (neutrophils), organelles, platelets
38
Toxic Shock LIKE syndrome (TSLS)
S. pyogenes Pyrogenic exotoxin (produces fever) Complication of invasive infection 30% mortality Hours to days Hypotension to organ failure SpeB and SpeC (superantigens)
39
Toxic Shock - S. aureus and S pyogenes
``` 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
Where is S. pyogenes normally found?
Pharynx
41
Variation of virulence factors caused by...
Variation in genes
42
Defence against infection
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
Competitive bacterial flora
Staph. epidermis Corynebacterium sp. (diphtheroids) Propionibacterium sp.
44
Medical name for a boil
Furuncle
45
When would you swab an ulcer/boi; etc
If lesion surface is broken/looks infected Pus or tissue if deeper lesion
46
Is Staph aureus coagulase negative or positive?
Positive. All other staph are coagulase negative.
47
Which species of Staphylococcus is Novobiocin resistant?
S. saprophyticus All other staph are SENSITIVE
48
Staph species
Gram positive cocci in clusters Aerobic and facultatively anaerobic
49
S. aureus
Clots plasma Causes wound, skin, bone and joint infections Enterotoxin - food poisoning SSSST PVL
50
Treatment for a staph aureus infection?
FLUCLOX FLUCLOX FLUCLOX
51
SSSST
Staphylococcal scalded skin syndrome toxin
52
If resistant to methicillin...it will be resistant to
Fluclox
53
Carbuncle
red, swollen, and painful cluster of boils that are connected to each other under the skin.
54
Staph aureus - skin infections
> Boils and carbuncles > Minor skin sepsis > Cellulitis > Infected eczema > Impetigo > Wound infection >Staphylococcal SSS
55
Classic sign of Impetigo
Golden crusting of lesions
56
MRSA treatmetn
Doxycycline Co-trimoxazole Clindamycin Vancomycin
57
Coagulase negative Staphs (Staph epidermidis)
> Skin commensals (not usually pathogenic) > Infection in association with implanted artificial material (heart valves, joints, IV catheters)
58
What can Staph. saprophyticus cause?
Urinary tract infection in women of child-bearing age.
59
Strep species
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
If bacteria appears as a "chain" and is beta haemolytic... what is it?
Group A Strep (GAS)
61
Beta-haemolytic Strep
> Pathogenic > Haemolysin is one of many toxins > Further classified by antigenic structure on surface - Group A - Group B
62
Group A strep
Throat | Severe skin infections
63
Group B strep
Meningitis in neonates
64
Important categories of alpha haemolytic strep
> Strep pneumoniae - pathogen, commonest, cause of pneumonia > Strep viridian's group - commensals of mouth, throat, vagina - cause infection, endocarditis
65
Non-haemolytic Streptococci
Enteroccus species (E. faecalis, E calcium) Commensals of bowel Common causes of UTI
66
Scalded Skin syndrome
Caused by staphylococcal infection Shearing/sloughing/peeling of skin Seen in children/new borns Sometimes seen in drug users
67
Strep pyogenes
GAS ``` Infected eczema Impetigo Cellulitis Erysipelas (superficial form of cellulitis) Necrotising fasciitis ```
68
Crepitus of muscles can be caused by?
Necrotising fasciitis
69
Strep pyogenes treatment
Penicillin | flucloxacillin too
70
Necrotising fasciitis treatment
Immediate surgical debridement as well as Abx
71
Necrotising fasciitis 2 types.
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
Fournier gangrene
Gangrene affecting the perineum More likely in diabetics
73
Tinea means...
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
Dermatophyte pathogenesis
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
Who is more commonly affected by dermatophyte infections?
Men | mainly foot and groin
76
Scalp ringworm normally affects...
Children
77
Sources of dermatophyte infection
* **other infected humans*** - antrhopophilic fungi Animals (cats, dogs, cattle) - zoophilic fungi Soil (less common UK) - geophilic fungi
78
Dermatophytes - causal organisms
**Trichophyton rubrum (human-human) ** Trichophyton mentagraphytes (next most common, human-human) Microsporum canis - cats, dogs, humans
79
Main cause of dermatophyte infection?
TRICHOPHYTON RUBRUM
80
Dermatophyte infection - diagnosis
Clinical appearance Woods light (fluorescence) Skin scrapings, nail clippings, hair - send to lab in a dermapak - culture takes 2 weeks+
81
When sending samples of suspected dermatophytes, what do you send them in?
Dermapaks.
82
Dermatophyte infection - treatment
> 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
Candida skin infection
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
Candida - treatment
Clotrimazole cream | Oral fluconazole
85
Scabies
Sarcoptes scabiei 6 weeks' incubation Intensely itchy rash affecting finger webs, wrists, genital area
86
Chronic crusted form of scabies =
Norwegian scabies
87
Scabies - treatment
Malathion lotion (applied to whole body, washed off next day) Benzyl benzoate (avoid in children)
88
What treatment should be avoided in children with scabies?
Benzyl benzoate
89
Lice infestation (pediculosis)
INTENSE ITCH Pediculis wapitis (head louse) Pediculus corporis (body louse) Phthirus pubis (pubic louse) Malathion for treatment
90
Lice - treatment
Malathion
91
Infection control - dermatology
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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