Skin and Soft Tissue Infections Flashcards
Skin anatomy (inside –> outside)
subcutaneous tissue
dermis
epidermis
Skin (function/protective mechanisms)
- serves as a barrier
- contains keratin (water-resistant)
- high salt and acidic pH
- normal flora: S. epi, CoNS, Propionibacterium, Corynebacterium, yeasts
Infections of the epidermis and dermis
- infection in/around hair follicles: folliculitis, furuncolosis, carbuncles
- infection of keratinized layer: dermatophyte fungi, Trichophyton, Epidermophyton, Microsporum
- infection of deeper layers: due to traumatic breaks in skin (erythrasma, hidradentis suppurativa, pilonidal cysts, sebaceous cysts)
Folliculitis, furuncolosis, carbuncles (causes)
- S. aureus is most common
- Enterobacteriaceae
- Pseudomonas aeruginosa associated with hot tubs
Trichophyton, Epidermophyton, Microsporum
- ringworm
- tinea pedis: athlete’s foot
- tinea versicolor: Malassezia furfur
Erythrasma
- chronic infection of keratinized layer
- Corynebacterium, Mycobacterium marinum
Hidradentis suppurativa
- obstructed apocrine gland (sweat gland)
- S. aureus, anaerobic strep, Bacteroides
pilonidal cysts
B. fragilis
Sebaceous cysts
Anaerobic cocci, bacteroides, propionibacterium, staphylococci, streptococci
Subcutaneous tissue infections
- abscesses, ulcers, boils: S. aureus, polymicrobial
- Erisipelas: cellulitis and streptococcal necrotizing fasciitis
Cellulitis
- usually in extremities, usually staph or strep
- anaerobic and aerobic mixed
- E. coli, Enterics, S. aureus, Strep, Anaerobes
Necrotizing fasciitis
- Group A Strep, S. aureus, Bacteroides, Clostridium
- Gas gangrene: C. perfringens
Infections of Muscle Fascia and Muscles
- Necrotizing fascitis
- Progressive bacterial synergistic gangrene (post-op infection, polymicrobial)
- Myositis
Myositis
- extensive muscle involvement
- S. aureus, Clostridium, Group A and B strep
- Virbio vulnificus, Aeromonas, other wound-associated bacteria
Wound Infections
- post-operative infections (normal flora or nosocomial organisms, S. aureus)
- human bite wounds (mouth flora, strep, S. aureus, Eikenella, Anaerobes)
- animal bite wounds (pasteurella, strep, staph, anaerobes)
- burns (Pseudomonas, S. aureus, Enterobacter, E. coli)
Organisms related to poor blood supply
S. aureus, S. pyogenes, Anaerobes
Organisms related to open ulcers
P. aeruginosa, Enterobacteriaceae, bowel flora in decubitus ulcers
Organisms related to draining sinuses/fistulas with bone involvement
S. aureus, Enterobacteriaceae, P. aeruginosa, anaerobes
Organisms related to Actinomycosis with or without bone involvement
Actinomyces, Propionibacterium, Prevotella, non-spore-forming anaerobes
Organisms related to breast abscesses
non-spore-forming anaerobes
Other organisms related to chronic draining sinuses/fistulas
Nocardia infections (brasiliensis)
Fistula infections
due to contamination with normal flora
Vesicles/Bullae
- fluid-filled lesion
- gram-stain
- S. aureus, Group A strep, P. aeruginosa, Vibrio vulnificus
- needle aspiration for fluid
Lymphadenitis
M. scrofulaceum, Group A strep, S. aureus, Y. pestis
Skin infections with bacteremia
- Petechiae with meningococcemia
- Cutaneous ulcers and Vibrio vulnificus sepsis
- S. aureus, P. aeruginosa, M. leprae, T. pallidum, Rickettsia, Systemic mycoses
Specimens to collect
- aspirates and exudates are best
Lab ID
- Direct smear: gram stain (or acid-fast if Myco)
- culture on plates (SBA, MAC, Choc, etc.)
- culture of viruses (look for cytopathic effect)
