Skin infections

Question 1

Main causative agents of skin infections

Answer 1

Staph aureus (catalase positive)
Strep pyogenes (catalase negative)

Both have hyaluronidase and haemolysin

Skin infections can result from trauma or haematogous spread

Question 2

Folliculitis

Answer 2

Infected hair follice
Staph aureus (or P. aeruginosa in hot tub folliculitis)
Pus is a result of immune response

Question 3

Furuncle

Answer 3

=deep foliculitis of one hair follice
common among the obese and those with diabetes
Usually require drainage unless smaller than 5mm
Patients at risk of endocarditis need antibiotics such as VANCOMYCIN and DAPTOMYCIN

Question 4

Carbuncle

Answer 4

=collection of furuncles
Connected SUBCUTANEOUSLY
needs surgical drainage as could cause sepsis

Question 5

Impetigo

Answer 5

Staph aureus and group A strep
Superficial skin infection due to access of subcorneal keratocytes
Highly contagious
Yellow scab
Nurseries and rugby players

Question 6

Staphylococcal scalded skin syndrome (SSSS)

Answer 6

NON SUPERFICIAL
caused by staphylococci
Create an exfoliate tissue which breaks down the desmosomes
Ritter’s disease in children. Cloxacillin used to treat it
High mortality in adults

Question 7

Erisipelas

Answer 7

affects the dermis and is a superficial form of cellulitis
Group A streptococci
Bright red lesion

Question 8

Cellulitis

Answer 8

Subcutaneous tissue = spreading infection of the skin
Can originate from boils and ulcers
Infection develops in a few hours to produce red, hot lesions
Strep pyogenes and staph aureus
Diabetic patients have particular problems with anaerobic cellulitis
Can lead to septicaemia

Question 9

Necrotising fascitis

Answer 9

Mixture of anaerobes and facultative anaerobes
highly toxic and causes widespread necrosis
Uncommon and severe
Affects the superficial and deep fascia causing the skin to come away
the skin must be removed

Question 10

Gangrene

Answer 10

Caused by clostridium spp
perfringens
necrosis and bubbling
doubling time of 12 mins

Question 11

Anthrax

Answer 11

Bacillus anthrax - gram positive sporing bacilli
spores found in soil, animal hides, bone meals and faeces
Cutaneous anthrax is rare and leads to black skin lesion

Question 12

Rickettsial infection

Answer 12

Rickettsia spp = obligate intracellular pathogen
Transmitted by fleas
Epidemic typhus is caused by Rickettsia prowazekii and the skin rash resembles typhoid.
Endemic typhoid cant be caused by Rickettsia typhus
Rocky mountain spotted fever; rickettsia rickettsii

Question 13

Cat and dogs bites

Answer 13

Pastrella multocida

Question 14

Rat bites

Answer 14

Spirillum mims

Streptobacillus moniliformis

Question 15

Human bites

Answer 15

Oral commensal microbiota

Eiherella corrodens

Question 16

Lymes disease

Answer 16

Spread by lxodestick and caused by Borellia burgodoferi= target shaped rash