Microbiology skin infections

Question 1

4 key presenting features of infection

Answer 1

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

Question 2

What is an exotoxin?

Answer 2

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

Question 3

What is an endotoxin?

Answer 3

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

Question 4

5 risk factors for bacteria skin infections

Answer 4

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

Question 5

What causes impetigo?

Answer 5

Staphylococcus aureus or Streptococcus pyogenes

Question 6

Describe impetigo presentation and epidemiology

Answer 6

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

Question 7

What is the difference between impetigo and ecthyma?

Answer 7

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

Question 8

How does ecthyma heal?

Answer 8

with scarring after eschar (black scab) falls off

Question 9

What is folliculitis?

Answer 9

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

Question 10

Describe furuncles in folliculitis

Answer 10

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

Question 11

Complication of folliculitis

Answer 11

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

Question 12

What layers does cellulitis affect?

Answer 12

all layers

Question 13

What layers does erysipelas affect?

Answer 13

lesion confined to dermis

Question 14

Describe how toxic shock syndrome occurs

Answer 14

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

Question 15

Toxic shock syndrome symptoms

Answer 15

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

Question 16

How is toxic shock syndrome diagnosed

Answer 16

bacterial swabs
blood cultures
blood tests
urinalysis

Question 17

Management of toxic shock syndrome

Answer 17

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

Question 18

How does meningococcal petechiae occur?

Answer 18

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

non-blanching rash

Question 19

What is necrotising fasciitis?

Answer 19

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

Question 20

What can the initial lesion be in necrotising fasciitis?

Answer 20

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

Question 21

Initial presentation of necrotising fasciitis and progression?

Answer 21

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

Question 22

Necrotising fasciitis causative organisms

Answer 22

Streptococcus pyogenes
Staphylococcus aureus
Vibrio vulnificus
Aeromonas hydrophila

Question 23

What is Fournier’s gangrene?

Answer 23

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

Question 24

List 5 types of specimens

Answer 24

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