Skin and Soft Tissue Infections Flashcards
What is the approximate surface area of the skin?
1.9 m^2
What is the role of skin?
- physical barrier against pathogens
2. protect from desiccation
What 3 things make up the skin?
- Dermis
- Epidermis
- Appendages - like hair follicles and sweat glands
SSTIs can be classified into two categories? What are they? what types of pathogens tend to cause each type?
- Simple Uncomplicated - mainly caused by gram positives
2. Complicated - caused by gram positives and gram negatives
What are 5 examples of SSTIs that are the simple uncomplicated type?
- Cellulitis
- Impetigo
- Erysipelas
- Simple abscesses
- Furuncles (boils)
What are 4 examples of SSTIs that are of the complicated type?
- Decubitus ulcers?
- Necrotizing fasciitis
- Cellulitis
- Gangrene
What two pathogens are primarily the cause of cellulitis?
Staph. aureus and group A strep like Strep. pyogenes
What tissues does cellulitis affect?
the dermis and the epidermis
What is the disease progression of cellulitis like? what systems are involved? What symptoms do people have?
Acute and spreading infection through the epidermis and dermis
Symptoms: Inflammation with little to no necrosis, edema, fever, chills, leukocytosis
there can be lymphatic involvement
What % of cellulitis cases result in bacteremia?
30%
What are two possible complication of cellulitis?
Abscess formation and osteomyelitis
What does impetigo look like (pustular) ?
red vesicules at different stages of development including pus-filled vesicles on an erythematous base and dry crusted lesions
what 5 pathogens tend to be involved in surgical wound infections? which is the most common?
#1. Staph aureus #2. Enterococci #3. Coag. neg staph #4. E.coli #5. Pseudomonas aeruginosa
What two types of pathogens are the most likely causes of traumatic wound infections? why?
S.aureus (getting in from the skin) and the Enterobacteriaceae (if the wound is exposed to dirt)
What 3 other pathogens (less frequent) can also cause traumatic wound infections? which is the most severe?
- Streptococci
- Clostridia
- Vibrio vulnificus (the worst)
How does someone become infected with Vibrio vulnificus?
when skin lacerations or abrasions come in direct contact with seawater containing V. vulnificus or as a result of penetrating marine injuries
What is the symptomatic progression of a Vibrio vulnificus infection?
- typically begin with swelling, redness, and intense pain around the infected site
- fluid filled blisters often then form
- Rapid progression to tissue necrosis that resembled gas gangrene
What symptom is common between V. vulnificus infections and necrotizing fasciitis that can differentiate them from cellulitis for example?
intense pain if the area of inflammation is touched
What % of patients with Vibrio vulnificus infections require surgical debridement?
50%
- lots end up needing amputation
What are 6 pathogens that can cause SSTIs in burn victims?
- S.aureus
- Enterobacter cloacae
- coag-neg Staphylococci
- P.aeruginosa
- E.coli
- Enterococcus spp.
What 3 pathogens are often involved in infections resulting from animal bites?
- Pasteurella maltocida
- Capnocytophaga canimorsus
- Eikenella corrodens
What two enzymes do Staphylococcal pathogens have that allow them to establish a local and systemic infection? Which enzyme does what?
- Coagulase: can lead to the formation of a fibrin coagulum, producing localized infection and protecting the organism from phagocytosis.
- Hyaluronidase: Hydrolyzes hyaluronic acids present in the intracellular matrix of connective tissue. can allow the organisms (like S. aureus) to disseminate through tissues
What kind of toxin is carried by Staph species on a plasmid? what disease does it cause?
Exfoliative toxin genes are carried on plasmids
cause Staphylococcal scalded skin syndrome (SSSS)
What is the result of exfoliative toxin on the skin (cellular and overall level) ?
Disturbance of the adherence of cells in the stratum granulosum layer of the epidermis.
Skin basically completely sloughs off `
What means of protection do older children and adults have against Staphylococcal scalded skin syndrome
Neutralizing antibodies formed after initial infection
What is the typical clinical presentation of SSSS?
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
What “super antigen” is almost exclusively associated with Staph aureus? Where is it occasionally found?
toxic shock toxin
Occasionally found in coagulase negative staph
What is different about the effect of a “super antigen”
- Massive polyclonal T cell activation
- up to 50% activated compared to 1/10’000 - Interacts directly with the T cell receptor
What are some symptoms caused by a super antigen?
nausea, vomiting, fever, capillary leakage (DIC), hypotension, shock, hypothermia
Which super antigen causes toxic shock syndrome?
TSST-1
What are the symptoms of toxic shock syndrome? what activates each one?
TSS produces fever, blood vesseldilation, and a sunburn-like rash.
cytokine stimulation results in hypotension and multi-organ failure
What group of strep does strep pyogenes belong to?
Group A strep
What 4 diseases are caused by S. pyogenes?
Pharyngitis (Strep throat)
Necrotizing fasciitis
Cellulitis
Toxic shock
What is the treatment for Necrotizing fasciitis? Why?
- Ceftriaxone (or high dose Penicillin) + clindamycin
- Clindamycin shuts down toxin production because it acts against the 50S ribosome which inhibits protein synthesis - IV-Ig
Which pathogen is responsible for 50% of infections resulting from dog bite wounds and is also the most common isolate from people hospitalized with infected bites?
Pasturella spp.
What kind of bacteria is Pasturella multocida? What atmospheric conditions does it like?
Small fastidious gram negative rod
Facultatively anaerobic
What two tests is P. multocida positive for?
Catalase and oxidase
What media support/dont support the growth of P. multocida?
Grows on SBA and Choc. Agar but not on MacConkey
What drug is Pasturella Multocida intrinsically resistant to?
Oral cephalosporins
What are the two species of Capnocytophaga that can cause infection? Which is worse?
C.canimorsus (fulminant sepsis 30% mortality)
C.cynodegmi (usually less severe limited infection)
What two tests are Capnocytophaga positive for?
Oxidase and catalase
What morphology do Capnocytophaga have?
Med to long fusoform gram - rods
What bacteria are associated with cat bites (and not dog bites)?
Bartonella henselae
What morphology does Bartonella henselae have?
Aerobic, fastidious gram negative cocco-bacilli
What two pathologies does B. henselae cause?
Cat scratch fever and endocarditis
What is the treatment for an infected cat-scratch
amoxicillin-clavulanic acid
Eikenella corrodens is the most common cause of infections resulting from?
Human bites and clenched fist injuries
What kind of bacteria is Eikenella corrodens?
a small, facultative gram negative rod
What are the catalase/oxidase test results for Eikenella corrodens? TSI?
Catalase negative and oxidase positive
No acid production on TSI
What growth requirements does E. corrodens have? What media will it not grow on?
requires hemin unless in 5-10% CO2
Won’t grow on MacConkey agar
What are two characteristic observations of E. corrodens grown in culture?
Pitting of the agar and bleach odour
What bacteria causes rat bite fever?
Streptobacillus monoliformis
What kind of bacteria is Strep. monoliformis?
Pleomorphic facultative gram negative rod
What are the results for a catalase/oxidase test for strep. monoliformis?
catalase and oxidase negative
What does Strep. monoliformis require for growth?
15% sheep / rabbit blood
Define: osteomyelitis. Where is it localized?
Inflammation of the bone
- may remain localized, or it may spread through the bone to involve the marrow, cortex, periosteum, and soft tissue surrounding the bone
What are the 3 ways in which an organism can reach the bone
- Directly through open wound/compound fracture
- Direct spread from neighbouring soft tissue infection
- Indirectly via the bloodstream (hematogenous)
Which is the most common route of infection for osteomyelitis? Which is the most acute?
Hematogenous spread is the most acute and the most common
What are the 3 criteria used to classify osteomyelitis?
- Duration and type of symptoms
- mechanism of infection
- Type of host response to infection
What 3 possible forms can osteomyelitis be classified into?
acute, subacute, or chronic
What are the #1 and #2 causes of osteomyelitis? bone-us (haha you’re stupid): what are 2 other bacteria that can cause it?
- Staph aureus
- Strep. pyogenes
H. influenzae, Gram-negative bacilli can also cause it
What is septic arthritis?
Inflammation of the joint spaces
How can septic arthritis be spread?
haematogenous or contiguous from soft tissue
What 3 bacteria can cause septic arthritis?
S. aureus, Streptococcus spp., Neisseria gonorrhoea
What is the cause of a diabetic foot infection? what is the progression of disease?
Cellulitis > Deep soft tissueinfection > Osteomyelitis
Peripheral vascular disease = loss of blood flow and innervation to the extremities leads to undetected injuries and infection
What are 3 risk factors for diabetic foot disease?
vascular disease
peripheral neuropathy
improper foot care
How do you treat diabetic foot infections? what organisms cause it?
Pretty much everything will cause it
Debridement and antibiotics
