Microbiology skin infections Flashcards

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1
Q

4 key presenting features of infection

A

rubor (redness)
calor (heat)
dolor (pain)
tumor (swelling)

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2
Q

What is an exotoxin?

A

produced inside most gram-positive bacteria as part of their growth + metabolism
released into surrounding medium

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3
Q

What is an endotoxin?

A

part of outer portion of the cell wall of gram-negative bacteria
liberated when bacteria die + cell wall breaks apart

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4
Q

5 risk factors for bacteria skin infections

A

people with DM
hospitalised/living in nursing homes
elderly
people with disorders of immune system
chemotherapy patients

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5
Q

What causes impetigo?

A

Staphylococcus aureus or Streptococcus pyogenes

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6
Q

Describe impetigo presentation and epidemiology

A

face of young children most commonly
limited to epidermis
erythematous papules that rapidly evolve into vesicles and pustules that rupture, forming yellow crusting lesions

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7
Q

What is the difference between impetigo and ecthyma?

A

ecthyma is a deeper infection than impetigo (invasion of dermis)

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8
Q

How does ecthyma heal?

A

with scarring after eschar (black scab) falls off

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9
Q

What is folliculitis?

A

infection of hair follicles
often caused by staphylococcus aureus or pseudomonas aeruginosa (contaminated hot spa water)

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10
Q

Describe furuncles in folliculitis

A

furuncles (boils) consist of walled-off collections of microorganisms associated with inflammatory cells in follicles and sebaceous glands that eventually ‘point’ and discharge pus

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11
Q

Complication of folliculitis

A

development of cluster of boils (carbuncle) on neck, back, or thighs, often with fever

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12
Q

What layers does cellulitis affect?

A

all layers

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13
Q

What layers does erysipelas affect?

A

lesion confined to dermis

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14
Q

Describe how toxic shock syndrome occurs

A

starts from localised staphylococcal infection
caused by release of exotoxins from toxigenic strains of bacteria staphylococcus aureus
rash that resembles sunburn followed by desquamation
generalised and palmar

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15
Q

Toxic shock syndrome symptoms

A

fever > 38.9
chills
headache
fatigue + feeling unwell
rash (red and flat) covers most of body
shedding of skin in large sheets
low BP, shock, renal + liver impairment
vomiting + diarrhoea
difficulty breathing
bleeding, bruising due to low platelets

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16
Q

How is toxic shock syndrome diagnosed

A

bacterial swabs
blood cultures
blood tests
urinalysis

17
Q

Management of toxic shock syndrome

A

removing source of infection eg. tampons
draining + cleaning wound site
IV fluids to treat shock
medications for very low BP
dialysis for renal failure
flucloxacillin, linezolid + 1st generation cephalosporin

18
Q

How does meningococcal petechiae occur?

A

lipooligosaccharide
endothelial damage
destruction of red cells
increased permeability and capillary leak (microhaemorrhages)
activation of coagulation
microvascular thrombosis

non-blanching rash

19
Q

What is necrotising fasciitis?

A

aggressive subcutaneous infection that tracks along the superficial fascia which comprises all tissue between skin and underlying muscles

20
Q

What can the initial lesion be in necrotising fasciitis?

A

can be trivial:
- minor abrasion
- insect bite
- injection site (drug addicts)
- boil
- can be no visible skin lesion

21
Q

Initial presentation of necrotising fasciitis and progression?

A

looks like cellulitis
can advance rapidly or slowly
progression = systemic toxicity - high temperatures, disorientation, lethargy
local examination = cutaneous inflammation, edema, discolouration/gangrene

22
Q

Necrotising fasciitis causative organisms

A

Streptococcus pyogenes
Staphylococcus aureus
Vibrio vulnificus
Aeromonas hydrophila

23
Q

What is Fournier’s gangrene?

A

associated with diabetes
extensive necrotising infection of genitals, perineal, scrotum and perianal region + groins
life threatening
male>female
polymicrobial necrotising fasciitis
Gram-negative, Group A strep, anaerobes

24
Q

List 5 types of specimens

A

scrapings
swabs - when exudate/pus
biopsies - tissues
swab for PCR
universal container - mites etc