Microbiology skin infections Flashcards
4 key presenting features of infection
rubor (redness)
calor (heat)
dolor (pain)
tumor (swelling)
What is an exotoxin?
produced inside most gram-positive bacteria as part of their growth + metabolism
released into surrounding medium
What is an endotoxin?
part of outer portion of the cell wall of gram-negative bacteria
liberated when bacteria die + cell wall breaks apart
5 risk factors for bacteria skin infections
people with DM
hospitalised/living in nursing homes
elderly
people with disorders of immune system
chemotherapy patients
What causes impetigo?
Staphylococcus aureus or Streptococcus pyogenes
Describe impetigo presentation and epidemiology
face of young children most commonly
limited to epidermis
erythematous papules that rapidly evolve into vesicles and pustules that rupture, forming yellow crusting lesions
What is the difference between impetigo and ecthyma?
ecthyma is a deeper infection than impetigo (invasion of dermis)
How does ecthyma heal?
with scarring after eschar (black scab) falls off
What is folliculitis?
infection of hair follicles
often caused by staphylococcus aureus or pseudomonas aeruginosa (contaminated hot spa water)
Describe furuncles in folliculitis
furuncles (boils) consist of walled-off collections of microorganisms associated with inflammatory cells in follicles and sebaceous glands that eventually ‘point’ and discharge pus
Complication of folliculitis
development of cluster of boils (carbuncle) on neck, back, or thighs, often with fever
What layers does cellulitis affect?
all layers
What layers does erysipelas affect?
lesion confined to dermis
Describe how toxic shock syndrome occurs
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
Toxic shock syndrome symptoms
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
How is toxic shock syndrome diagnosed
bacterial swabs
blood cultures
blood tests
urinalysis
Management of toxic shock syndrome
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
How does meningococcal petechiae occur?
lipooligosaccharide
endothelial damage
destruction of red cells
increased permeability and capillary leak (microhaemorrhages)
activation of coagulation
microvascular thrombosis
non-blanching rash
What is necrotising fasciitis?
aggressive subcutaneous infection that tracks along the superficial fascia which comprises all tissue between skin and underlying muscles
What can the initial lesion be in necrotising fasciitis?
can be trivial:
- minor abrasion
- insect bite
- injection site (drug addicts)
- boil
- can be no visible skin lesion
Initial presentation of necrotising fasciitis and progression?
looks like cellulitis
can advance rapidly or slowly
progression = systemic toxicity - high temperatures, disorientation, lethargy
local examination = cutaneous inflammation, edema, discolouration/gangrene
Necrotising fasciitis causative organisms
Streptococcus pyogenes
Staphylococcus aureus
Vibrio vulnificus
Aeromonas hydrophila
What is Fournier’s gangrene?
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
List 5 types of specimens
scrapings
swabs - when exudate/pus
biopsies - tissues
swab for PCR
universal container - mites etc
