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Microbiology > Exam #8: Bacterial Infections of the Skin & Soft Tissue I > Flashcards

Exam #8: Bacterial Infections of the Skin & Soft Tissue I Flashcards

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Biology 101 flashcards
1
Q

What organisms is DM a risk factor for?

A

S. aureus
GBS
Anaerobes
Gram negative bacteria

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2
Q

What organisms is neutropenia a risk factor for?

A

Pseudomonas aeruginosa

*Note that hot tub exposure is also a major risk factor for the development of P. aeruginosa infection

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3
Q

What organisms is IV drug abuse a risk factor for?

A

MRSA

P. aeruginosa

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4
Q

What is impetigo?

A

Most superficial of bacterial skin infections that causes:

  • Honey crusted lesions*
  • Bullae (blisters)
  • Erosions

Often seen around the mouth

*Most common in children & S. aureus causes 80% of cases (2nd is GAS)

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5
Q

What is Bullous Impetigo?

A

S. aureus that causes blisters initially filled with cloudy fluid that later rupture resulting in erosions and crusting

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6
Q

What causes Bullous Impetigo?

A

Exfoliative toxin of S. aureus

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7
Q

What is Ecthmya?

A
  • Deeper form of impetigo that results in scarring and ulceration– this may result from neglected of inadequately treated impetigo
  • Causes “punched-out” ulcerative lesions

*Seen in the homeless population

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8
Q

What is a furuncle?

A

Deep-steated infection of the hair follicle caused by S. aureus

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9
Q

What is a carbuncle?

A
  • Multiple coalesced furuncles/boils that extend into deeper subcutaneous tissue caused mainly by S. aureus
  • Extends deeper into subcutaneous tissue

The defining feature of a carbuncle is when a patient presents with chills and fever

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10
Q

What is Folliculitis?

A

Infection/ Inflammation of the hair follicles that is most commonly caused by P. aerugenosa

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11
Q

What are Erysipelas?

A
  • Erysipelas is an acute infection of the skin that is characterized by distinct borders between the involved skin and the uninvolved skin.
  • Most commonly caused by S. pyogenes
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12
Q

What is cellulitis?

A
  • Cellulitis is a skin infection that involves deeper subcutaneous tissue
  • BOTH local inflammation & systemic inflammation are seen (fever)

*In contrast to erysipelas, in cellulitis it is v. difficult to differentiate between the involved & uninvolved areas

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13
Q

What organisms cause cellulitis? Why is it important to differentiate between them?

A
  • Cellulitis is most commonly caused by S. pyogenes (GAS), followed by S. aureus
  • However:
    1) Dog or cat bite= Pasteurella multocida
    2) Saltwarer= Vibrio vulnificus

*Differentiation is important for treatment; remember to start broad and then narrow abx selection

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14
Q

What is a Paronychia?

A

Localized & superficial infection or abscess of the nailfolds

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15
Q

What is the difference between acute & chronic paronychia?

A 
Acute= bacteria (S. aureus) 
Chronic= fungi (c. albicans)
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16
Q

What is Necrotizing Fasciitis?

A
  • Acute infection of subcutaneous tissue that leads to destruction of muscle & fat
  • It presents as cellulitis followed by bullae & gangrene
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17
Q

How is Necrotizing Fasciitis treated?

A

Surgical debridement & antibiotics

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18
Q

List the characteristics of S. aureus.

A
  • Gram (+) cocci in clusters “grape-like”
  • Catalase +
  • Coagulase +
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19
Q

How is S. aureus transmitted?

A

Nasal Shedding

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20
Q

List the diseases that are caused by S. aureus.

A 
Skin infections 
Sepsis 
Endocarditis 
Pneumonia 
Osteomyelitis 
Septic Arthritis 
Purulent Meningitis 
Food Poisoning 
Toxic Shock
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21
Q

Describe S. aureus in culture.

A

Aureus= “gold” i.e. golden colonies

B-hemolytic (complete hemolysis)

22
Q

What are the virulence factors associated with the structure of S. aureus?

A 
Capsule= anti-phagocytic 
Biofilm 
Peptidoglycan (TLR)= endotoxin like acticity 
Teichoic Acid (Adhesion)
Protein A
23
Q

What is the mechanism of Protein A?

A
  • Protein A inhibits antibody mediated clearance by binding to IgG Fc domain (links to the phagocyte)
  • Basically turns the antibody around so that it can no longer link to a phagocyte
24
Q

What are the toxins associated with S. aureus?

A

Cytotoxins
Exfoliative toxins
Enterotoxins
TSST-1

25
Q

What cytotoxin is associated with S. aureus?

A

Alpha toxin= pore forming

26
Q

What are the Exfoliative toxins associated with S. aureus?

A

Serine proteases that split desmosoe junction in the epithelial layer

*This is what mediates the symptoms that are seen in “Staph Scalded Skin Syndrome”

27
Q

What enzymes associated with S. aureus are virulence factors?

A

There are a variety of enzymes that can hydrolyze host tissue to aid in the spread of S. aureus throughout the body

  • Coagulase= converts fibirinogen to fibrin
  • Hyaluronidase= hydrolyzes HA in connective tissue, promoting spread
  • Fibrinolysin= Dissolves fibrin clots
  • Lipases= hydrolyzes lipids
  • Nucleases= hydrolyzes DNA
28
Q

Outline the pathogenesis of S. aureus.

A

1) Staph adheres to the cell via Tiechoic acid
2) Secretes alpha toxin that forms pores to enter the cell
3) Produces Protein A that “sops up antibody” and prevents macrophage mediated clearance

29
Q

List the toxin mediated diseases that are caused by S. aureus.

A

Scalded Skin Syndrome
Food poisoning
Toxic Shock

30
Q

List the infectious diseases that are caused by S. aureus.

A 
Impetigo
Folliculitis 
Furuncles 
Carbuncles 
Osteomyelitis 
Septic arthritis
31
Q

What is Scalded Skin Syndrome?

A

Sloughing off of the superficial layer of the skin that looks like a sunburn in the absence of sun exposure

  • Toxin mediated disease
  • Typically seen in infants
  • Nasal transmission
  • Starts on face and mouth and then spreads to the rest of the body

*Note that you CANNNOT see S. aureus in culture in this syndrome

32
Q

What causes Scalded Skin Syndrome?

A

Exfoliative toxin (ETA or ETB)

*Serine proteases that break apart desmosomes

33
Q

Can S. aureus be cultured from skin in Scalded Skin Syndrome?

A

No–this is toxin mediated

*Note that there also is no leukocytosis

34
Q

How does Scalded Skin Sydrome recover?

A

Neutralizing Antibodies that are produced by the baby

35
Q

List the stages of Scalded Skin Sydrome.

A

1) Initial (red rash)
2) Exfoliative
3) Desquamative

36
Q

What is a Nikolsky sign?

A

Skin desquemation with minimal pressure from the examiner

*This is pathognomonic for SSSS

37
Q

How is SSSS managed?

A

1) Fluid resuscitation
2) Correction of electrolyte imbalance
3) Abx including oxacillin or vancomycin

38
Q

How is SSSS diagnosed?

A
  • Presentation

- Skin Biopsy

39
Q

Will a skin culture of folliculitis, impetigo or furuncle/ carbuncles be positive for S. aureus?

A

Yes–these diseases are caused by infection, NOT toxin

40
Q

How are furuncles & carbuncles treated?

A
  • I&D/ remove foreign body

- Antibiotics–nafcillin, oxacillin, cefazolin

41
Q

What is MRSA? How did MRSA come to be?

A

Methecillin Resistant S. Aureus

  • B-Lactamase (hydrolyzes B-lactam ring of PCN)
  • MecA gene acquired on a mobile genetic element is a PBP with low affinity for the semi-synthetic PCNs
42
Q

Where are most community acquired MRSA infections acquired?

A

Skin

43
Q

How is MRSA treated?

A

Vancomycin

44
Q

What is Osteomyelitis?

A

Skin and soft tissue infection that has progressed into a bone

45
Q

What are the symptoms of Osteomyelitis?

A

Bone pain
Fever
Swelling
Malaise

46
Q

What are the risk factors associated with Osteomyelitis?

A

Anything that is going to impair blood flow to the bone:

  • Sickle cell anemia
  • Injury
  • FB
  • IV drug use
  • DM
  • Kidney dialysis
  • Surgical procedures to bony areas
  • Untreated infections of tissue near a bone
47
Q

What is the most common causes of Osteomyelitis?

A

S. aureus is the most likely cause of osteomyelitis

48
Q

What is septic arthritis?

A
  • Painful, erythematous joint with purulent material obtained on aspiration
  • Usually seen in the large joints (shoulder, knee, hip, elbow)
49
Q

What is the most common cause of septic arthritis in children & adults receiving intraarticular injections?

A

S. aureus

50
Q

What is the most common causative organism in sexually active women?

A

Neisseria gonorrheae

51
Q

Generally, how are non-MRSA S. aureus skin infections treated?

A

Penicillinase-resistant PCN (nafcillin & oxacillin)

MRSA= Vancomycin

Microbiology (49 decks)

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