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Microbiology > Exam #8: SSTI II > Flashcards

Exam #8: SSTI II Flashcards

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1
Q

List the characteristics of S. pyogenes.

A
  • Gram (+) cocci in chains
  • Catalase negative
  • Group B
  • Lancefield A
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2
Q

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

A 
A= green, partial hemolysis
B= complete hemolysis 
G= no hemolysis
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3
Q

What are the Lancefield antigens?

A
  • 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
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4
Q

What is the strep. associated with Lancefield A?

A

S. pyogenes (which is Beta-hemolytic)

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5
Q

What is the strep. associated with Lancefield B?

A

S. agalactiae

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6
Q

What is the strep. associated with Lancefield D?

A

S. bovis

Enterococcus

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7
Q

What infections are caused by GAS?

A

Remember GAS= S. pyogenes:

Strep throat
Skin & soft tissue infection
Rheumatic Fever
Glomerulonephritis

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8
Q

How is GAS transmitted?

A

Respiratory droplets or breaks in the skin

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9
Q

What is the capsule associated with GAS?

A

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

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10
Q

What are the adhesins associated with GAS?

A

F protein
M protein
LTA protein

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11
Q

What is M protein?

A

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

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12
Q

What toxins are associated with GAS?

A
  • Streptolysin O & S= pore forming toxins for invasion of host & destruction of tissue
  • Superantigens
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13
Q

What are the functions of Streptolysin O & S?

A

Pore-forming

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14
Q

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

A
  • 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
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15
Q

Describe the pathogenesis of GAS.

A

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

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16
Q

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

A

Impetigo
Erysipelas
Cellulitis
Necrotizing Fasciitis

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17
Q

What is Impetigo?

A
  • 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

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18
Q

What is Erysipelas?

A
  • 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
Q

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

A
  • Cellulitis has a deeper involvement and is NOT well demarcated
  • S. pyogenes
20
Q

What is Necrotizing fasciitis?

A

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
Q

What is the presentation of Nec. Fas.?

A
  • Initially grey skin

- Pain out of proportion to exam

22
Q

How is Nec. Fas. treated?

A

Surgical debridement
Skin grafting
Antibiotics

23
Q

What are the characteristics of Scarlet Fever?

A
  • Complication of GAS
  • Caused by TOXIN released by GAS
  • Diffuse erythematous rash
  • Strawberry tongue
24
Q

What is Rheumatic Fever?

A
  • Complication of S. pyogenes pharyngitis

- Characterized by inflammatory changes involving the heart, joints, blood vessels, and subcutaneous tissue

25
Q

What is Glomerulonephritis?

A

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
Q

What are the symptoms of post-streptococcal glomerulonephritis?

A

Hematuria
Edema
HTN

27
Q

How is post-streptococcal glomerulonephritis diagnosed?

A

There will be evidence of recent streptococcal infection via serology: (though skin infection will be gone)

  • Anti-streptolysin O antigen
  • Reduced serum complement
28
Q

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

A
  • Superantigen induced shock and organ failure

- Most patients with streptococcal TSS are bacteremic & have nec. fas.

29
Q

How is streptococcal skin infection diganosed?

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

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

30
Q

How is S. pyogenes infection treated?

A

PCN

31
Q

List the characteristics of P. aeruginosa.

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

*Makes pyocyanin (blue-green pigment)

32
Q

When is P. aeruginosa most commonly seen?

A

Opportunistic pathogen; patient already has infection

33
Q

Is P. aeruginosa capsulated?

A

Yes, mucoid polysaccharide capsule

34
Q

What toxin is associated with P. aeruginosa?

A

Exotoxin A

35
Q

What is the mechanism of Exotoxin A?

A
  • A/B Toxin that inactivates EF-2 via ADP ribosylation & blocks protein synthesis
  • Similar to the Diptheria toxin
36
Q

List the infections that are caused by P. aeruginosa

A

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
Q

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

A

Ecthyma gangrenosum

38
Q

What is Ecthyma gangrenosum?

A

Purple macule that develops rapidly into a hemorrhagic bulla that ruptures

39
Q

What is Pseudomonas folliculitis?

A

“Hot tub” folliculitis

*Pseudomonas can withstand very high temperatures and chlorine

40
Q

What causes “green nails” associated with P. aeruginosa?

A
  • 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
Q

What is webspace intertrigo?

A

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

42
Q

How is P. aeruginosa treated?

A
  • Varies with presentation

- Abx resistance is a huge problem

43
Q

How is P. aeruginosa infection prevented?

A
  • Prevention of contaminated medical equipment & nosocomial transmission
  • Maintain dry conditions

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

Microbiology (49 decks)

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