Exam #8: SSTI II Flashcards Preview

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Flashcards in Exam #8: SSTI II Deck (43):
1

List the characteristics of S. pyogenes.

- Gram (+) cocci in chains
- Catalase negative
- Group B
- Lancefield A

2

What is the difference between a, b, & g hemolysis?

A= green, partial hemolysis
B= complete hemolysis
G= no hemolysis

3

What are the Lancefield antigens?

- Lancefield antigens are named after the woman that discovered them, Rebecca Lancefield
- These are group specific cell wall carbohydrate structures used to define species of Strep.
- Mostly refers to beta-hemolytic strep

4

What is the strep. associated with Lancefield A?

S. pyogenes (which is Beta-hemolytic)

5

What is the strep. associated with Lancefield B?

S. agalactiae

6

What is the strep. associated with Lancefield D?

S. bovis
Enterococcus

7

What infections are caused by GAS?

Remember GAS= S. pyogenes:

Strep throat
Skin & soft tissue infection
Rheumatic Fever
Glomerulonephritis

8

How is GAS transmitted?

Respiratory droplets or breaks in the skin

9

What is the capsule associated with GAS?

HA capsule (looks like self; we don't make antibodies)

10

What are the adhesins associated with GAS?

F protein
M protein
LTA protein

11

What is M protein?

Myosin-like protein that facilitates adhesion, anti-phagoyctosis, and prevents complement activation
- variable regions are associated with differential virulence

12

What toxins are associated with GAS?

- Streptolysin O & S= pore forming toxins for invasion of host & destruction of tissue
- Superantigens

13

What are the functions of Streptolysin O & S?

Pore-forming

14

List three other virulence factors associated with GAS and their functions.

- Strep Super Antigens (SAgs), which are superantigens that increase proinflammatory cytokine production (Scarlet Fever, STS, & nec. fas)
- C5a peptidase= degrades chemotactic C5a
- DNAse= depolymerize DNA in pus decreasing viscosity
- Streptokinase= cleaves plasminogen

15

Describe the pathogenesis of GAS.

1) M-protein mediates adhesion
2) Streptolysin-O forms pores in the membrane
3) Entry
4) C5a blocks recruitment of neutrophils

16

List the skin & soft tissue infections that can be caused by GAS.

Impetigo
Erysipelas
Cellulitis
Necrotizing Fasciitis

17

What is Impetigo?

- Honey crusted lesions most seen around the mouth
- Most commonly caused by S. aureus but also caused by S. pyogenes

*Note that if you culture and see Gram (+) cocci, you WILL NOT know the difference; also, bullous impetigo is not seen in s. pyogenes

18

What is Erysipelas?

- Bright red appearance of the involved skin which forms a plateau of sharply demarcated tissue from the surrounding normal skin
- Most commonly caused by S. pyogenes
- Can be associated with fever

19

What is the difference between Erysipelas and cellulitis? What is the most common cause of cellulitis?

- Cellulitis has a deeper involvement and is NOT well demarcated
- S. pyogenes

20

What is Necrotizing fasciitis?

A severe infection said to be caused by "flesh-eating bacteria"
- Most commonly caused by S. pyogenes
- Secondarily caused by S. aureus

*Pain and tenderness are SEVERE; pain out of proportion to exam initially

21

What is the presentation of Nec. Fas.?

- Initially grey skin
- Pain out of proportion to exam

22

How is Nec. Fas. treated?

Surgical debridement
Skin grafting
Antibiotics

23

What are the characteristics of Scarlet Fever?

- Complication of GAS
- Caused by TOXIN released by GAS

- Diffuse erythematous rash
- Strawberry tongue

24

What is Rheumatic Fever?

- Complication of S. pyogenes pharyngitis
- Characterized by inflammatory changes involving the heart, joints, blood vessels, and subcutaneous tissue

25

What is Glomerulonephritis?

Type III Hypersensitivity that usually follows cutaneous infection
- Antigen/ ab complexes activate complement in the kidney
- Seen 3-6 weeks following GAS skin infection

26

What are the symptoms of post-streptococcal glomerulonephritis?

Hematuria
Edema
HTN

27

How is post-streptococcal glomerulonephritis diagnosed?

There will be evidence of recent streptococcal infection via serology: (though skin infection will be gone)
- Anti-streptolysin O antigen
- Reduced serum complement

28

What is Streptococcal Toxic Shock Syndrome? How is this different from the TSS that is seen with S. aureus?

- Superantigen induced shock and organ failure
- Most patients with streptococcal TSS are bacteremic & have nec. fas.

29

How is streptococcal skin infection diganosed?

- Culture followed by Lancefield (A i.e. GAS)
- Direct Ag detection
- PCR

Anti-streptolysin O (ASO) antibodies in serum (ASO)= previous exposure

30

How is S. pyogenes infection treated?

PCN

31

List the characteristics of P. aeruginosa.

Gram (-) rod
Non-fermenter
Oxidase +
Motile
Hemolytic

*Makes pyocyanin (blue-green pigment)

32

When is P. aeruginosa most commonly seen?

Opportunistic pathogen; patient already has infection

33

Is P. aeruginosa capsulated?

Yes, mucoid polysaccharide capsule

34

What toxin is associated with P. aeruginosa?

Exotoxin A

35

What is the mechanism of Exotoxin A?

- A/B Toxin that inactivates EF-2 via ADP ribosylation & blocks protein synthesis
- Similar to the Diptheria toxin

36

List the infections that are caused by P. aeruginosa

Skin and soft tissue infections in the immunocompromised:
- Burn victims
- Cystic fibrosis patients

Folliculitis
Osteochondritis (penetrating injury) caused by a penetrating injury when the person is wearing a sock

37

How does bacteremia in the presence of P. aeruginosa present?

Ecthyma gangrenosum

38

What is Ecthyma gangrenosum?

Purple macule that develops rapidly into a hemorrhagic bulla that ruptures

39

What is Pseudomonas folliculitis?

"Hot tub" folliculitis

*Pseudomonas can withstand very high temperatures and chlorine

40

What causes "green nails" associated with P. aeruginosa?

- This is essentially a paronychia that is caused by Pseudomonas infection
- Pyocyanin in P. aerugenosa causes the nails to turn green
- Seen in patients with wet hands

41

What is webspace intertrigo?

Eroded space between toes that is most commonly caused by P. aeruginosa

42

How is P. aeruginosa treated?

- Varies with presentation
- *Abx resistance is a huge problem*

43

How is P. aeruginosa infection prevented?

- Prevention of contaminated medical equipment & nosocomial transmission
- Maintain dry conditions

*Note that unnecessary use of broad-spectrum antibiotics can select for resistant organisms

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