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

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Flashcards in Exam #8: Bacterial Infections of the Skin & Soft Tissue I Deck (51):
1

What organisms is DM a risk factor for?

S. aureus
GBS
Anaerobes
Gram negative bacteria

2

What organisms is neutropenia a risk factor for?

Pseudomonas aeruginosa

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

3

What organisms is IV drug abuse a risk factor for?

MRSA
P. aeruginosa

4

What is impetigo?

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)

5

What is Bullous Impetigo?

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

6

What causes Bullous Impetigo?

Exfoliative toxin of S. aureus

7

What is Ecthmya?

- 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

8

What is a furuncle?

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

9

What is a carbuncle?

- 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*

10

What is Folliculitis?

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

11

What are Erysipelas?

- 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

12

What is cellulitis?

- 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

13

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

- 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

14

What is a Paronychia?

Localized & superficial infection or abscess of the nailfolds

15

What is the difference between acute & chronic paronychia?

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

16

What is Necrotizing Fasciitis?

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

17

How is Necrotizing Fasciitis treated?

Surgical debridement & antibiotics

18

List the characteristics of S. aureus.

- Gram (+) cocci in clusters "grape-like"
- Catalase +
- Coagulase +

19

How is S. aureus transmitted?

Nasal Shedding

20

List the diseases that are caused by S. aureus.

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

21

Describe S. aureus in culture.

Aureus= "gold" i.e. golden colonies
B-hemolytic (complete hemolysis)

22

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

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

23

What is the mechanism of Protein 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

What are the toxins associated with S. aureus?

Cytotoxins
Exfoliative toxins
Enterotoxins
TSST-1

25

What cytotoxin is associated with S. aureus?

Alpha toxin= pore forming

26

What are the Exfoliative toxins associated with S. aureus?

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

What enzymes associated with S. aureus are virulence factors?

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

Outline the pathogenesis of S. aureus.

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

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

Scalded Skin Syndrome
Food poisoning
Toxic Shock

30

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

Impetigo
Folliculitis
Furuncles
Carbuncles
Osteomyelitis
Septic arthritis

31

What is Scalded Skin Syndrome?

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

What causes Scalded Skin Syndrome?

Exfoliative toxin (ETA or ETB)

*Serine proteases that break apart desmosomes

33

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

No--this is toxin mediated

*Note that there also is no leukocytosis

34

How does Scalded Skin Sydrome recover?

Neutralizing Antibodies that are produced by the baby

35

List the stages of Scalded Skin Sydrome.

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

36

What is a Nikolsky sign?

Skin desquemation with minimal pressure from the examiner

*This is pathognomonic for SSSS

37

How is SSSS managed?

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

38

How is SSSS diagnosed?

- Presentation
- Skin Biopsy

39

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

Yes--these diseases are caused by infection, NOT toxin

40

How are furuncles & carbuncles treated?

- I&D/ remove foreign body
- Antibiotics--nafcillin, oxacillin, cefazolin

41

What is MRSA? How did MRSA come to be?

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

Where are most community acquired MRSA infections acquired?

Skin

43

How is MRSA treated?

Vancomycin

44

What is Osteomyelitis?

Skin and soft tissue infection that has progressed into a bone

45

What are the symptoms of Osteomyelitis?

Bone pain
Fever
Swelling
Malaise

46

What are the risk factors associated with Osteomyelitis?

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

What is the most common causes of Osteomyelitis?

S. aureus is the most likely cause of osteomyelitis

48

What is septic arthritis?

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

49

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

S. aureus

50

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

Neisseria gonorrheae

51

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

Penicillinase-resistant PCN (nafcillin & oxacillin)

MRSA= Vancomycin

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