Skin and Soft Tissue Infections

Question 1

Simple uncomplicated SSTIs

Answer 1

Mostly Gram +
Cellulitis, impetigo, erysipelas, simple abscess, furuncles (boils)
Means they’re not very deep (just dermal or epidermal layer)

Question 2

Complicated SSTIs

Answer 2

Gram + and -
Decubitus ulcers, necrotizing faciitis, cellulitis, gangrene
Much deeper, into fascia or muscle

Question 3

Cellulitis

symptoms, complications, causes, treatment

Answer 3

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

Question 4

Pustular impetigo

Answer 4

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

Question 5

5 bacteria that cause surgical wound infections

Answer 5

S. aureus
Enterococci
Coag neg staph
E. coli
P. aeruginosa

Question 6

2 most common bacteria for traumatic wounds

Answer 6

S. aureus

Enterobacteriaceae

Question 7

Vibrio vulnificus
(how do you get it, morphology, symptoms, treatment)

Answer 7

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

Question 8

What is a good diagnostic clue for both V. vulnificus and necrotising faciitis?

Answer 8

Pain is more severe than what it should be from just looking at the wound

Question 9

5 bacteria from bites

Answer 9

Pasteurella maltocida
Capnocytophaga canimorsus
Eikenella corrodens
Peptostreptococci
Alpha and Beta streptococci

Question 10

Hyaluronidase

Answer 10

Hydrolyzes hyaluronic acids present in the intracellular matrix of connective tissue
Can disseminate
S. aureus

Question 11

Coagulase

Answer 11

May lead to the formation of a fibrin coagulum, producing localized infection and protecting the organism from phagocytosis
S. aureus

Question 12

Exfoliative toxin (SSSS)

Answer 12

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

Question 13

Staphlococcal scalded skin syndrome

Answer 13

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

Question 14

Toxic shock toxin

Answer 14

Responsible for toxic shock syndrome
Considered a super antigen
Usually associated with S. aureus and occasionally in coag neg staph

Question 15

Super antigens

Answer 15

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

Question 16

Toxic shock syndrome

Answer 16

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%

Question 17

S. pyogenes

Answer 17

Group A strep

Causes: pharyngitis, necrotising faciitis, cellulitis, toxic shock

Question 18

Treatment for group A necrotising faciitis

Answer 18

High dose penicillin or ceftriaxone and clindamycin

Clindamycin binds to the 50S ribosome and shuts down toxin production

Question 19

Where is Pasturella found?

Answer 19

Responsible for 50% of infections resulting from dog bite wounds
Most common isolate

Question 20

Pasteurella multocida
(morphology, growth, catalase, oxidase, TSI, odor, resistant to)

Answer 20

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

Question 21

What is Pasteurella multocida intrinsically resistant to?

Answer 21

Oral cephalosporins

Question 22

Capnocytophaga

growth, morphology, species, oxidase, catalase, serious disease in

Answer 22

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

Question 23

Bartonella henselae
(how do you get it, growth, morphology, causes, diagnosis)

Answer 23

Cat bites
Aerobic, fastidious gram negative cocco-bacilli
Hemin dependent, 15-45 days growth
Cat scratch fever, endocarditis
Rarely cultured, use serological diagnosis

Question 24

What do you use to treat Pasteurella/Capno/Bartonella?

Answer 24

Amoxicillin/clavulinic acid

Question 25

Eikenella corrodens
(morphology, catalase, oxidase, growth, TSI, odour, how do you get it)

Answer 25

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

Question 26

Streptobacillus monoliformis
(causes, how do you get it, morphology, growth, catalase, oxidase)

Answer 26

Rat bites
Rat bite fever
Pleomorphic facultative gram negative rod
Requires 15% sheep/rabbit blood for growth
Catalase and oxidase -
Biochemically inert

Question 27

3 paths organisms can reach the bone through

Answer 27

1. directly through a skin wound communicating with bone (open fracture)
2. direct spread from a neighbouring soft tissue infection or adjacent infective focus
3. indirectly via the blood stream (hematogenous spread - more acute and most common)

Question 28

Septic arthritis
(where does it infect, how, 3 species that cause it)

Answer 28

Infection of joint spaces
Hematogenous or contiguous
S. aureus, Strep spp., gram negative bacilli

Question 29

Osteomyelitis

where does it infect, how, 5 bacteria that cause it

Answer 29

Infection of the bone
Hematogenous or contiguous
S. aureus, S. pyogenes, CNS, H influenzae, gram negative bacilli

Question 30

Mr Smith comes in with hip replacement, goes home, returns 8 months later with hip infection. Is it S. aureus or coag neg staph?

Answer 30

Coag neg staph. S.aureus is very virulent and will declare itself within a couple weeks

Question 31

2 most common causes of osteomyelitis

Answer 31

1. S. aureus

2. Coag neg staph