Skin and Soft Tissue Infections Flashcards
Simple uncomplicated SSTIs
Mostly Gram +
Cellulitis, impetigo, erysipelas, simple abscess, furuncles (boils)
Means they’re not very deep (just dermal or epidermal layer)
Complicated SSTIs
Gram + and -
Decubitus ulcers, necrotizing faciitis, cellulitis, gangrene
Much deeper, into fascia or muscle
Cellulitis
symptoms, complications, causes, treatment
Acute, spreading infectious process affecting epidermis and dermis Inflammation with little or no necrosis, edema Lymphatic involvement Fever, chills, leukocytosis Bacteremia up to 30% of cases Complications: abscess and osteomyelitis Caused by: S. aureus, and S. pyogenes Treat with 1st generation cephalosporin
Pustular impetigo
Acute process but can see them in different stages
Very superficial
Danger is getting a secondary infection
Pus filled vesicles on an erythematous base and dry crusted lesions
5 bacteria that cause surgical wound infections
S. aureus Enterococci Coag neg staph E. coli P. aeruginosa
2 most common bacteria for traumatic wounds
S. aureus
Enterobacteriaceae
Vibrio vulnificus (how do you get it, morphology, symptoms, treatment)
Salt water wounds
Can cause really bad infections
Gram negative bacilli, oxidase positive
Infections typically begin with swelling, redness, and intense pain around the infected site
Fluid filled blisters often develop and progress to tissue necrosis in a rapid process resembling gas gangrene
Pain is more severe than what it should be from just looking at the wound!
Many patients require surgical debridement or amputation
What is a good diagnostic clue for both V. vulnificus and necrotising faciitis?
Pain is more severe than what it should be from just looking at the wound
5 bacteria from bites
Pasteurella maltocida Capnocytophaga canimorsus Eikenella corrodens Peptostreptococci Alpha and Beta streptococci
Hyaluronidase
Hydrolyzes hyaluronic acids present in the intracellular matrix of connective tissue
Can disseminate
S. aureus
Coagulase
May lead to the formation of a fibrin coagulum, producing localized infection and protecting the organism from phagocytosis
S. aureus
Exfoliative toxin (SSSS)
Genes are carried on plasmids
Mechanism of action is unknown
Leads to disturbance of the adherence of cells in the stratum granulosum layer of the epidermis
Neutralizing antibodies develop after infection, protecting older children and adults
Gives staphlococcal scalded skin syndrome
Staphlococcal scalded skin syndrome
Due to the exfoliative toxin
Characterized by the abrupt onset of a localized peri-oral erythema (redness and inflammation around the mouth) that covers the entire body within 2 days
Large bullae or cutaneous blisters form soon thereafter and are followed by desquamation of the epithelium
Scarring is not seen because the separation occurs at a very superficial layer
Toxic shock toxin
Responsible for toxic shock syndrome
Considered a super antigen
Usually associated with S. aureus and occasionally in coag neg staph
Super antigens
Interacts directly with T cell receptor, causes massive polyclonal T-cell stimulation
Excessive release can cause nausea, vomiting, fever, capillary leakage, hypotension, shock
Up to 50% of T cells are activated
Toxic shock syndrome
Systemic absorption of TSST-1
TSS produces fever, blood vessel dilation, and a sunburn-like rash
Cytokine stimulation gives hypotension, multi-organ failure
Fatality around 15%
S. pyogenes
Group A strep
Causes: pharyngitis, necrotising faciitis, cellulitis, toxic shock
Treatment for group A necrotising faciitis
High dose penicillin or ceftriaxone and clindamycin
Clindamycin binds to the 50S ribosome and shuts down toxin production
Where is Pasturella found?
Responsible for 50% of infections resulting from dog bite wounds
Most common isolate
Pasteurella multocida (morphology, growth, catalase, oxidase, TSI, odor, resistant to)
Small fastidious gram negative rod Facultatively anaerobic Catalase and oxidase + Grows on both SBA and chocolate agar TSI slant A/A MacConkey rarely supports growth Characteristic odor Intrinsically resistant to oral cephalosporins
What is Pasteurella multocida intrinsically resistant to?
Oral cephalosporins
Capnocytophaga
growth, morphology, species, oxidase, catalase, serious disease in
CO2 loving
Medium to long fusoform gram negative rods
Dogs and cats
C. canimorsus (fulminant sepsis 30% mortality)
C. cynodegmi (usually less severe limited infection)
Oxidase and catalase +
Serious disease in asplenic patients or the immunocompromised
Bartonella henselae (how do you get it, growth, morphology, causes, diagnosis)
Cat bites
Aerobic, fastidious gram negative cocco-bacilli
Hemin dependent, 15-45 days growth
Cat scratch fever, endocarditis
Rarely cultured, use serological diagnosis
What do you use to treat Pasteurella/Capno/Bartonella?
Amoxicillin/clavulinic acid
Eikenella corrodens (morphology, catalase, oxidase, growth, TSI, odour, how do you get it)
Small, facultative gram negative rods Catalase NEGATIVE, oxidase + Require hemin unless in 5-10% CO2 No growth on MacConkey No acid on TSI slant Characteristic bleach odor Pitts the agar Human bites, clenched fist injuries
Streptobacillus monoliformis (causes, how do you get it, morphology, growth, catalase, oxidase)
Rat bites
Rat bite fever
Pleomorphic facultative gram negative rod
Requires 15% sheep/rabbit blood for growth
Catalase and oxidase -
Biochemically inert
3 paths organisms can reach the bone through
- directly through a skin wound communicating with bone (open fracture)
- direct spread from a neighbouring soft tissue infection or adjacent infective focus
- indirectly via the blood stream (hematogenous spread - more acute and most common)
Septic arthritis (where does it infect, how, 3 species that cause it)
Infection of joint spaces
Hematogenous or contiguous
S. aureus, Strep spp., gram negative bacilli
Osteomyelitis
where does it infect, how, 5 bacteria that cause it
Infection of the bone
Hematogenous or contiguous
S. aureus, S. pyogenes, CNS, H influenzae, gram negative bacilli
Mr Smith comes in with hip replacement, goes home, returns 8 months later with hip infection. Is it S. aureus or coag neg staph?
Coag neg staph. S.aureus is very virulent and will declare itself within a couple weeks
2 most common causes of osteomyelitis
- S. aureus
2. Coag neg staph
