Skin and soft tissue infections Flashcards
What are the main organisms that colonise the skin?
- Coagulase-negative Staphylococci
- S Aureus
- Propionibacterium (e.g. Acnes)
- Corynebacterium
What is the pathogenesis of skin infections?
Inoculation
- penetrate skin with contaminated objects
- Contamination of pre-existing breach in skin surface
Other route - neuronal migration in herpes simplex
Systemic/generalised infection
What viral infections cause skin infections?
Herpes simplex virus
VZV - shingles
Molluscum contagiosum
Cow pox - first virus to be vaccinated
Orf- sheets/goats - purulent producing papule
What is the pathogenesis of the HSV?
Vesicle formation -> ulceration -> weeping vesicular lesions (virus release)
Gains entry through sensory nerve endings and remains in dorsal root ganglion
Latent = episome - no immune repose
Reactivation - migrates downward to sensory root ends and manifests
What are the two types of HSV infection
Primary - occurs once - usually in infancy, extensive painful lesions in mouth
Secondary - occurs time again - weeping vesicles (peri oral and genital)
What triggers a reactivation infection of HSV?
Stress or infection
What is the type of herpes that MAINLY causes a) mouth herpes; b) genital herpes
HSV1 (mouth)
HSV2 (genital)
How his herpes simplex virus diagnosed?
Clinical usually
Vesicle fluid releases virus (PCR detection of viral DNA)
What is the treatment fora) cold sores and b) genital herpes
a) topical acyclovir
b) oral acyclovir
What is the primary and secondary manifestations of VZV
a) chicken pox
b) shingles
How does latent infection of VZV present?
Shingles - weeping vesicular rash
Dermatome distribution
How is VZV diagnosed?
Clinical
Vesicle fluid - PCR VZV DNA
What is the treatment for shingles
Acyclovir/valacyclovir - Oral/IV
How does the molluscum contagiosum virus present?
Raised PEARLY lesions
Umbilicated
How is molloscum contagious diagnosed?
Clinical - very simple
What is the treatment for molloscum contagiosum treated?
None - usually disappear with 6-18 months
What are the main causative organisms for bacterial skin infections?
Staph Aureus
Strep Pyogenes
Also H influenzae, pasteurella multocida (cat/dogs)
What type of bacteria is staph areus? What exotoxins does it produce that are important in the context of skin infections?
Gram positive- normal nasal flora (30% pop)
- epidermolytic toxin A and B (ETA/ETB)
- Toxic shock syndrome toxin
- Paton valentine leucocidin (PVL)
What is the main action of strep pyogenes?
Haemolytic
What is the causative bacteria that cause impetigo?
S aureus
S Pyogenes
How does impetigo present?
Usually on face (around nose -mainly children) - infection of epidermis
Plaque-like lesions
Yellowish exudate
Thick scabs - honey comb lesions
How is impetigo diagnosed?
Clinical
Bacterial culture
What are the complications of impetigo? What is the pathogenesis?
Bullous impetigo
Staphylococcal scalded skin syndrome (SSSS)
Exotoxin - Epidermolytic toxin A&B
What area of skin and bodily areas mainly is effected by erysipelas?
Dermis
Face and shin
What is the causative bacteria for erysipelas?
S Pyogenes
How does erysipelas present?
Lymph node enlargement
Fever and malaise
Well demarcated inflamed lesion - red, swollen, painful, hot
What is cellulitis?
Infection of the skin and subcutaneous tissue?
What are the causative organisms for cellulitis?
P Aureus
S Pyogenes
H influenzae
Pasturella multocida (animal bites)
How does cellulitis present?
Site of inoculation (portal of entry may not be observable!)
Diffuse enlargement - not well demarcated - erythema (redness), swelling, tenderness, hot
Any part of body - UNILATERAL
Fever and malaise
How is cellulitis diagnosed?
- Clinical diagnosis
- Unilateral (discount bilateral differentials)
- Lesion swabs
- Blood cultures (rare though)
What is the pathogen causing anthrax?
Bacillus anthracis
- spore forming aerobic gram positive
Where is the source for anthrax?
Imported wool, hides, hair, drum skins
What is the pathogenesis of anthrax?
Inoculation through breaks in the skin
How does anthrax present?
Malignant pustule
When is anthrax lethal?
If inhaled/septicaemic
Cutaneous = readily treated
What are the two types of necrotising fascitis and what bacteria causes them?
Type 1 - polymicrobrial - anaerobes, gram negative bacilli (from large bowel)
Type 2 - strep pyogenes
How does necrotising fascitis present?
Dark, rapidly spreading necrotising lesion
Fever and malaise (very sick!)
What is the treatment of necrotising fascitis?
IV antibiotics
Surgical debridement
What is the causative organism for gas gangrene?
Clostridium perfrinigens - anaerobic gram positive
Dirty lower GI procedures/limb amputation
How does gas gangrene present and whats its treatment?
Subcutaneous gas
Dark rapidly spreading necrotising
IV antibiotics and limb debridement
When should topical/ora/IV antibiotics be used?
Topical - superficial infections e.g. impetigo erysipelas
Oral/IV = more severe - cellulitis/necrotising fascitis/gas gangrene etc
What is the treatment for staph aureus/strep pyogenes
Penecillin (flucloxacillin)
Allergy -erythromycin/calrithromycin vancomycin, linezoid
MRSA - vancomycin, linezoid
What antibiotics are used to treat anaerobic infections?
Metronidazole
What antibiotics should we use for necrotising facilities?
Meropenem
Clindamycin
What are skin fungal infections referred to as? What is there pathogenisis
Dermatophyte infections
Use keratin as nutritional substrate
What are the name of dermatophyte infections?
Skin
- Tina corporis
- Tina pedis (athletes foot)
Scalp Tina capitus (ring worm)
