Skin and soft tissue infection Flashcards
why is the skin intrinsically resistant to infection
- low water content
- low pH
- low temp
- high salt
- fats and FAs have antimicrobial properites
- microbiota
what are the common skin microbiota
- staph epidermidis
- staph aureus
- diptheroids
- streptococci
- some gram bacilli (pseudomonas)
- anaerobes
- yeasts
what are the main bacteria that cause skin and soft tissue infections
Staph aureus strep pygogenes clostridia psuedomonas sp. other gram -ves
what are the main fungi that cause skin and soft tissue infections
candida and filamentous fungi
what are the main parasites that cause skin and soft tissue infections
Leishmania
schistosomes
hookworms
what are the main antrhopods that cause skin and soft tissue infections
insects, ticks, mites
what are the main viruses that cause skin and soft tissue infections
- HSV
- VZV
- HPV
- measles
- rubella
- enteroviruses
- parvovirus
molluscum contagiosum
what are the bacterial localised infections of soft tissue and skin
folliculitis
abscess
what are the bacterial spreading infections of soft tissue and skin
impetigo
cellulitis
what are the bacteria necrotising infections of soft tissue and skin
fasciitis
most common cause of folliculitis
staph aureus
what is the proper name of a boil
furuncle
what is the important staph species that causes UTI
staph saphrophyticus
how can you tell the difference in culture of staph aureus and staph epidermidis
aureus - coagulase positive
epidermidis - coagulase negative
primary defense against staph aureus is via which arm of the immune system
innate - neutrophils
explain the pathogenesis of staph aureus
- binds via adhesins
- inhibits chemotaxis via CHIPS
- inhibits phagocytosis
- if ingested - can resist killing
- biofim formation
- abscess formation
what substances does staph aureus make that allows it to inhibit phagocytosis
- capsule
- protein A (binds Fc end of Ab)
- staphylokinase
- complement inhibitors
- haemolysins and leukocidins - kill neutrophils
community acquired MRSA is commonly associated with which virulence factor
Panton-Valentine leukocidin
what is impetigo
an infection of the epidermis characterised by bullous, crusted or pustular lesions
impetigo is caused by…
staph aureus or Strep pyogenes
staph aureus = bullous impetigo
what is erysipelas
a rapidly spreading superficial erythematous infection with well defined borders, plus pain and fever
what is the difference between erysipelas and cellulitis
cellulitis also involves the subcutaneous fat
what is the main cause of erysipelas and cellulitis
Strep pyogenes
most common causes of necrotising
strep pyogenes and anaerobes (including Clostridium)
most common cause of gas gangrene
Clostridia
what are the substances produced by strep pyogenes that help it evade the innate immune system
- M protein, capsule = antiphagocytic
- leukocidal toxins
- DNAse - overcomes NETS
- C5a peptidase - evades C’
how does strep pyogenes cause damage
- direct cytolethal toxins and enzymes
- superantigens
- activation of autoimmunity
explain structure of clostridia
gram positive rods, anaerobe, spore-forming
what things would you perform on a skin swab of someone with a skin/soft tissue infection
- nucleic acid testing (viruses)
- microscopy (gram stain - bacteria)
- culture and identification
- antimicrobial susceptibility testing (bacteria)
treatment of impetigo
soap and water + mupirocin (if mild) or flucloxacillin/dicloxacillin (if more severe) - (unless strep pyogenes alone)
treatment of cellulitis
flucloxacillin or dicloxacillin (unless Strep pyogenes alone)
treatment of gas gangrene
surgery + penicillin G +/- hyperbaric oxygen
treatment of diabetic foot ulcer
co-amoxyclav + metronidazole
