62 Skin + soft tissue infections Flashcards
Which organisms typically colonise the skin? (4)
Coagulase negative staphylococci.
Staph aureus.
Propionibacterium spp.
Corynebacterium spp.
Which viruses cause skin infections? (6)
Herpes simplex virus. Herpes zoster virus. Molluscum contagiosum. Human Papilloma virus. Orf. Cowpox.
What kind of skin infection does HSV cause?
1o: painful + extensive lesions inside mouth.
2o: perioral weeping + vesicular lesions.
How is Herpes Simplex diagnosed?
Clinical.
Difficult cases: vesicle fluid PCR.
How is HSV treated?
Cold sores: topical acyclovir.
Genital herpes: oral acyclovir.
How does herpes zoster infection present?
Diagnosis?
Treatment?
Weeping vesicular rash with dermatomal distribution.
Clinical.
Aciclovir/valaciclovir.
What causes molluscum contagiosum?
The pox virus.
Appearance of molluscum contagious infection?
Diagnosis?
Treatment?
Raised pearly lesions up to 3mm. Umbilicated.
Clinical.
None - physical rx if disfiguring.
Which virulence factors does staph aureus produce? (3)
DNAase,
Coagulase,
Teichoic acid.
Which exotoxins does staph aureus produce? (3)
Epidermolytic toxins A + B
Toxic Shock Syndrome Toxin.
Pantun-Valentine leukocidin.
Which virulence factors does s pyogenes produce? (7)
Adhesins M proteins Hyaluronic acid capsule Hyaluronidase C5a peptidase Streptolysins O and S Pyogenic exotoxins
What is impetigo?
Causes? (2)
Lesion appearance?
Infection of the epidermis. (Often at site of skin damage).
Staph aureus, Strep pyogenes.
Plaque like, yellowish, thick “honey crusted”
What are the complications of an impetigo infection?
Pathogenesis?
Bullous impetigo, Staphylococcal Scalded Skin Syndrome.
Epidermolytic toxins inactivate glycoprotein desmoglein-1 (required for cell-cell adhesion).
What is erysipelas?
Causative agent?
History?
Infection of the dermis.
Strep pyogenes.
At skin damage site, often face/neck. Preceeded by pain.
What is seen on examination in erysipelas? (3)
Fever, malaise.
Well demarcated inflamed lesion (red + hot).
Lymph node enlargement.
What is cellulitis?
Causative agents? (4)
Infection of the skin and subcutaneous tissue. Staph aureus. Strep pyogenes. Pasteurella multocida. Haemophilus influenzae.
What is seen on examination in cellulitis?
Fever, malaise.
Diffuse inflamed lesion.
Anthrax organism?
Appearance?
Epidemiology?
Sites of infection?
Bacillus anthracis.
Malignant pustule/ eschar (black).
West African drum use, IVDU’s.
Cutaneous ( 1% mortality) vs inhlational/septicaemic (45% mortality).
What are the causes of necrotising fasciitis?
Type 1: Polymicrobial: anaerobes, enteric gram -ve bacilli.
Type 2: Strep pyogenes.
Necrotising fasciitis: examination:
Diagnosis:
Treatment:
Fever, malaise, dark rapidly spreading necrotic lesion.
Rx on suspicion, but microscopy + culture.
IV meropenem + clindamycin + surgical debridement.
Gas gangrene. Organism:
Examination:
History:
Rx:
Clostridium perfringens (anaerobic g+ve bacillus). Palpable subcutaneous gas. Dark + necrotic lesion. Post operative (lower GI or amputees). IV antibiotics (metronidazole) + surgical debridement.
What is the empiric therapy for skin infections?
Flucloxacillin.
Pen allergy: eryro/claryhtromycin, vacomcin, linezolid.
How are high MRSA risk skin infections treated? (2)
Vancomycin.
Linezolid.
Causative agents of dermatophyte infections? (2)
Pathogenesis:
Tricophyton spp. Microsporum spp.
Keratin = nutritional substrate. Restricted to stratum corneum, rarely penetrate living cells.
How are dermatophyte infections diagnosed?
Microscopy + culture of skin scrapings.
How are fungal skin infections treated? (2)
Topical antifungals:
Clotrimazole. Terbinafine.
How are fungal scalp and nail infections treated? (3)
Systemic antifungals:
Terbinafine. Itraconazole. Griseofulvin.
