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Clinical Micro > Skin and Soft Tissue Infections > Flashcards

Skin and Soft Tissue Infections Flashcards

1
Q

What is the approximate surface area of the skin?

A

1.9 m^2

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2
Q

What is the role of skin?

A
  1. physical barrier against pathogens

2. protect from desiccation

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3
Q

What 3 things make up the skin?

A
  1. Dermis
  2. Epidermis
  3. Appendages - like hair follicles and sweat glands
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4
Q

SSTIs can be classified into two categories? What are they? what types of pathogens tend to cause each type?

A
  1. Simple Uncomplicated - mainly caused by gram positives

2. Complicated - caused by gram positives and gram negatives

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5
Q

What are 5 examples of SSTIs that are the simple uncomplicated type?

A
  1. Cellulitis
  2. Impetigo
  3. Erysipelas
  4. Simple abscesses
  5. Furuncles (boils)
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6
Q

What are 4 examples of SSTIs that are of the complicated type?

A
  1. Decubitus ulcers?
  2. Necrotizing fasciitis
  3. Cellulitis
  4. Gangrene
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7
Q

What two pathogens are primarily the cause of cellulitis?

A

Staph. aureus and group A strep like Strep. pyogenes

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8
Q

What tissues does cellulitis affect?

A

the dermis and the epidermis

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9
Q

What is the disease progression of cellulitis like? what systems are involved? What symptoms do people have?

A

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

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10
Q

What % of cellulitis cases result in bacteremia?

A

30%

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11
Q

What are two possible complication of cellulitis?

A

Abscess formation and osteomyelitis

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12
Q

What does impetigo look like (pustular) ?

A

red vesicules at different stages of development including pus-filled vesicles on an erythematous base and dry crusted lesions

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13
Q

what 5 pathogens tend to be involved in surgical wound infections? which is the most common?

A 
#1. Staph aureus 
#2. Enterococci 
#3. Coag. neg staph 
#4. E.coli 
#5. Pseudomonas aeruginosa
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14
Q

What two types of pathogens are the most likely causes of traumatic wound infections? why?

A

S.aureus (getting in from the skin) and the Enterobacteriaceae (if the wound is exposed to dirt)

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15
Q

What 3 other pathogens (less frequent) can also cause traumatic wound infections? which is the most severe?

A
  1. Streptococci
  2. Clostridia
  3. Vibrio vulnificus (the worst)
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16
Q

How does someone become infected with Vibrio vulnificus?

A

when skin lacerations or abrasions come in direct contact with seawater containing V. vulnificus or as a result of penetrating marine injuries

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17
Q

What is the symptomatic progression of a Vibrio vulnificus infection?

A
  1. typically begin with swelling, redness, and intense pain around the infected site
  2. fluid filled blisters often then form
  3. Rapid progression to tissue necrosis that resembled gas gangrene
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18
Q

What symptom is common between V. vulnificus infections and necrotizing fasciitis that can differentiate them from cellulitis for example?

A

intense pain if the area of inflammation is touched

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19
Q

What % of patients with Vibrio vulnificus infections require surgical debridement?

A

50%

- lots end up needing amputation

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20
Q

What are 6 pathogens that can cause SSTIs in burn victims?

A
  1. S.aureus
  2. Enterobacter cloacae
  3. coag-neg Staphylococci
  4. P.aeruginosa
  5. E.coli
  6. Enterococcus spp.
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21
Q

What 3 pathogens are often involved in infections resulting from animal bites?

A
  1. Pasteurella maltocida
  2. Capnocytophaga canimorsus
  3. Eikenella corrodens
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22
Q

What two enzymes do Staphylococcal pathogens have that allow them to establish a local and systemic infection? Which enzyme does what?

A
  1. Coagulase: can lead to the formation of a fibrin coagulum, producing localized infection and protecting the organism from phagocytosis.
  2. Hyaluronidase: Hydrolyzes hyaluronic acids present in the intracellular matrix of connective tissue. can allow the organisms (like S. aureus) to disseminate through tissues
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23
Q

What kind of toxin is carried by Staph species on a plasmid? what disease does it cause?

A

Exfoliative toxin genes are carried on plasmids

cause Staphylococcal scalded skin syndrome (SSSS)

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24
Q

What is the result of exfoliative toxin on the skin (cellular and overall level) ?

A

Disturbance of the adherence of cells in the stratum granulosum layer of the epidermis.

Skin basically completely sloughs off `

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25
Q

What means of protection do older children and adults have against Staphylococcal scalded skin syndrome

A

Neutralizing antibodies formed after initial infection

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26
Q

What is the typical clinical presentation of SSSS?

A

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

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27
Q

What “super antigen” is almost exclusively associated with Staph aureus? Where is it occasionally found?

A

toxic shock toxin

Occasionally found in coagulase negative staph

28
Q

What is different about the effect of a “super antigen”

A
  1. Massive polyclonal T cell activation
    - up to 50% activated compared to 1/10’000
  2. Interacts directly with the T cell receptor
29
Q

What are some symptoms caused by a super antigen?

A

nausea, vomiting, fever, capillary leakage (DIC), hypotension, shock, hypothermia

30
Q

Which super antigen causes toxic shock syndrome?

A

TSST-1

31
Q

What are the symptoms of toxic shock syndrome? what activates each one?

A

TSS produces fever, blood vesseldilation, and a sunburn-like rash.

cytokine stimulation results in hypotension and multi-organ failure

32
Q

What group of strep does strep pyogenes belong to?

A

Group A strep

33
Q

What 4 diseases are caused by S. pyogenes?

A

Pharyngitis (Strep throat)
Necrotizing fasciitis
Cellulitis
Toxic shock

34
Q

What is the treatment for Necrotizing fasciitis? Why?

A
  1. Ceftriaxone (or high dose Penicillin) + clindamycin
    - Clindamycin shuts down toxin production because it acts against the 50S ribosome which inhibits protein synthesis
  2. IV-Ig
35
Q

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?

A

Pasturella spp.

36
Q

What kind of bacteria is Pasturella multocida? What atmospheric conditions does it like?

A

Small fastidious gram negative rod

Facultatively anaerobic

37
Q

What two tests is P. multocida positive for?

A

Catalase and oxidase

38
Q

What media support/dont support the growth of P. multocida?

A

Grows on SBA and Choc. Agar but not on MacConkey

39
Q

What drug is Pasturella Multocida intrinsically resistant to?

A

Oral cephalosporins

40
Q

What are the two species of Capnocytophaga that can cause infection? Which is worse?

A

C.canimorsus (fulminant sepsis 30% mortality)

C.cynodegmi (usually less severe limited infection)

41
Q

What two tests are Capnocytophaga positive for?

A

Oxidase and catalase

42
Q

What morphology do Capnocytophaga have?

A

Med to long fusoform gram - rods

43
Q

What bacteria are associated with cat bites (and not dog bites)?

A

Bartonella henselae

44
Q

What morphology does Bartonella henselae have?

A

Aerobic, fastidious gram negative cocco-bacilli

45
Q

What two pathologies does B. henselae cause?

A

Cat scratch fever and endocarditis

46
Q

What is the treatment for an infected cat-scratch

A

amoxicillin-clavulanic acid

47
Q

Eikenella corrodens is the most common cause of infections resulting from?

A

Human bites and clenched fist injuries

48
Q

What kind of bacteria is Eikenella corrodens?

A

a small, facultative gram negative rod

49
Q

What are the catalase/oxidase test results for Eikenella corrodens? TSI?

A

Catalase negative and oxidase positive

No acid production on TSI

50
Q

What growth requirements does E. corrodens have? What media will it not grow on?

A

requires hemin unless in 5-10% CO2

Won’t grow on MacConkey agar

51
Q

What are two characteristic observations of E. corrodens grown in culture?

A

Pitting of the agar and bleach odour

52
Q

What bacteria causes rat bite fever?

A

Streptobacillus monoliformis

53
Q

What kind of bacteria is Strep. monoliformis?

A

Pleomorphic facultative gram negative rod

54
Q

What are the results for a catalase/oxidase test for strep. monoliformis?

A

catalase and oxidase negative

55
Q

What does Strep. monoliformis require for growth?

A

15% sheep / rabbit blood

56
Q

Define: osteomyelitis. Where is it localized?

A

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

57
Q

What are the 3 ways in which an organism can reach the bone

A
  1. Directly through open wound/compound fracture
  2. Direct spread from neighbouring soft tissue infection
  3. Indirectly via the bloodstream (hematogenous)
58
Q

Which is the most common route of infection for osteomyelitis? Which is the most acute?

A

Hematogenous spread is the most acute and the most common

59
Q

What are the 3 criteria used to classify osteomyelitis?

A
  1. Duration and type of symptoms
  2. mechanism of infection
  3. Type of host response to infection
60
Q

What 3 possible forms can osteomyelitis be classified into?

A

acute, subacute, or chronic

61
Q

What are the #1 and #2 causes of osteomyelitis? bone-us (haha you’re stupid): what are 2 other bacteria that can cause it?

A
  1. Staph aureus
  2. Strep. pyogenes

H. influenzae, Gram-negative bacilli can also cause it

62
Q

What is septic arthritis?

A

Inflammation of the joint spaces

63
Q

How can septic arthritis be spread?

A

haematogenous or contiguous from soft tissue

64
Q

What 3 bacteria can cause septic arthritis?

A

S. aureus, Streptococcus spp., Neisseria gonorrhoea

65
Q

What is the cause of a diabetic foot infection? what is the progression of disease?

A

Cellulitis > Deep soft tissueinfection > Osteomyelitis

Peripheral vascular disease = loss of blood flow and innervation to the extremities leads to undetected injuries and infection

66
Q

What are 3 risk factors for diabetic foot disease?

A

vascular disease
peripheral neuropathy
improper foot care

67
Q

How do you treat diabetic foot infections? what organisms cause it?

A

Pretty much everything will cause it

Debridement and antibiotics

Clinical Micro (28 decks)

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