Updated: 2/28/2019

Streptococcus pyogenes (Group A Streptococci)

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Key Images
https://upload.medbullets.com/topic/104030/images/group a strep classification - moises.jpg
https://upload.medbullets.com/topic/104030/images/streptococcal_hemolysis.jpg
https://upload.medbullets.com/topic/104030/images/streptococcal_pharyngitis.jpg
https://upload.medbullets.com/topic/104030/images/strawberrytongue.jpg
https://upload.medbullets.com/topic/104030/images/osc_microbio_21_02_impetigo.jpg
https://upload.medbullets.com/topic/104030/images/scarlet_fever_2.jpg
Snapshot
  • A 6-year-old boy presents to his pediatrician for sore throat and a headache. His symptoms began approximately 2 days ago and have not improved. The mother reports that the patient appears uncomfortable and feels warm. She says that he was born at 39-weeks gestation via a normal spontaneous vaginal delivery with no complications. He has received all of his vaccinations appropriate for his age. He has no significant past medical history and only takes a daily multivitamin. He has no allergies to medications known to the mother. Physical examination is notable for perioral crusted lesions with tonsilar swelling with exudates. A rapid antigen detection test is positive for Streptococcal pyogenes infection. He is started on oral penicillin.
Introduction
  • Classification
    • gram-positive cocci
  • Microbiology
    • reservoir
    • properties
      • Lacefield group A
      • β-hemolytic 
      • bacitracin sensitive
      • pyrrolidonyl arylamidase (PYR) positive
      • hyaluronic acid capsule
        • inhibits phagocytosis
      • M protein 
        • major virulence factor that inhibits complement activation and protects against phagocytosis  
        • plasma cells create antibodies against this protein for opsonization
          • via molecular mimicry, this can lead to acute rheumatic fever 
      • streptolysin O
        • an oxygen labile enzyme that destroys both red and white blood cells, giving this organism its β-hemolytic property
        • antibodies against streptolysin O (anti-ASO antibodies) allows checking ASO titers to determine if there was a recent Streptococcus pyogenes infection
      • DNase B
        • antibodies against DNase B (anti-DNase B) also indicate recent Streptococcus pyogenes infection
      • pyogenic exotoxin (erythrogenic toxin)
        • can result in scarlet fever
        • can superstimulate T-cells, resulting in streptococcal toxic shock syndrome
  • Associated conditions
    • streptococcal pharyngitis
    • streptococcal skin infections
    • Scarlet fever
    • delayed antibody-mediated reactions
      • rheumatic fever
      • poststreptococcal glomerulonephritis
Presentation
 
Diseases Associated with Streptococcal Pyogenes
Disease
Presentation
Diagnostic Studies Treatment
Streptococcal pharyngitis
  • Symptoms
    • sore throat
    • headache
  • Physical exam
    • tonsillar enlargement without or with exudates 
    • fever
    • lymphadenopathy
  • Rapid antigen detection test (RADT)
    • high specificity (~95%)
  • Throat culture
    • high sensitivity (90-95%)
  • Penicillin
    • prompt treatment prevents the development of rheumatic fever  
Skin infections
  • Symptoms/physical exam
    • folliculitis
      • infection of the hair follicle
    • cellulitis
      • erythematous, edematous, and warm skin 
    • impetigo 
      • vesicular and blistered skin lesions that flakes 
        • typically found by the mouth
  • Gram stain and culture
  • Dicloxacillin
    • covers both Streptococcus pyogenes and Staphylococcus aureus
Scarlet fever 
  • Symptoms/physical exam 
    • scarlet red rash 
      • begins on the trunk and neck and then spreads to the extremities
      • a sand paper-like rash
    • strawberry tongue 
    • fever
  • Gram stain and culture
  • Penicillin 
Rheumatic fever
  • Symptoms/physical exam
    • fever
    • chest pain (secondary to myocarditis)
    • arthritis (acute migratory polyarthritis)
    • chorea
      • dance-like movements of the extremities (2-3 weeks post pharyngitis
  • Note that many years after the myocarditis, patients can develop rheumatic valvular disease
    • the mitral valve is most commonly affected and the aortic valve is the second most common
  • Clinical diagnosis
    • typically seen in untreated cases of streptococcal pharyngitis 
    • based on the Jones criteria
      • having 2 major manifestations or 1 major manifestation plus 2 minor manifestations classifies the patient as having acute rheumatic fever
  • Major manifestations
    • carditis/valvulitis
    • arthritis
    • Sydenham chorea
  • Minor manifestations
    • arthralgia
    • fever
  • Antibiotic prophylaxis with penicillin
    • the goal is to prevent recurrent streptococcal pharyngitis and acute rheumatic fever in order to decrease the risk of damaging the heart and its valves further
Poststreptococcal glomerulonephritis 
  • Symptoms/physical exam
    • generalized edema
    • hematuria
    • hypertension
  • Based on both clinical and laboratory findings
    • laboratory findings
      • positive throat or skin culture
      • positive anti-ASO antibodies or streptozyme test
  • Penicillin if the streptococcal infection is still present
  • Supportive therapy
 
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(M1.MC.14.157) Part of the success of the Streptococcus pyogenes bacterium lies in its ability to evade phagocytosis. Which of the following helps in this evasion? Tested Concept

QID: 101616
1

M protein

77%

(53/69)

2

Streptolysin O

13%

(9/69)

3

Streptolysin S

0%

(0/69)

4

Pyrogenic toxin

1%

(1/69)

5

Streptokinase

6%

(4/69)

M 1 D

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(M1.MC.13.15) About two weeks ago, an 11-year-old boy fell from his bicycle into some rose bushes and received superficial lacerations on his hands and arms. His mother bandaged up his wounds, and after a week she noticed that a localized pustular rash with yellow crusts developed on his right forearm (see Figure A). The child was taken to the pediatrician and a wound culture was taken that showed catalase-negative, beta-hemolytic Gram-positive cocci in chains. Which of the following agents is responsible for the infection? Tested Concept

QID: 101474
FIGURES:
1

Sporothrix schenckii

15%

(5/34)

2

Streptococcus mitis

3%

(1/34)

3

Streptococcus mutans

3%

(1/34)

4

Staphylococcus epidermidis

9%

(3/34)

5

Streptococcus pyogenes

68%

(23/34)

M 2 E

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(M1.MC.13.152) A 10-year-old male is taken to his physician by his parents due to a sore throat. A throat swab and culture reveal the growth seen in Figure A. The bacteria are gram-positive and bacitracin inhibits their growth. The child is given treatment and sent home. Twenty years later, the patient presents to the emergency department with dyspnea on exertion and CXR showed an enlarged cardiac silhouette and pulmonary edema. The patient's current symptomatology most likely occurred secondary to which of the following? Tested Concept

QID: 101611
FIGURES:
1

Type III hypersensitivity reaction

21%

(8/39)

2

Coagulase activity

3%

(1/39)

3

Leukocidin activity

5%

(2/39)

4

Type I hypersensitivty reaction

0%

(0/39)

5

Molecular mimicry

72%

(28/39)

M 1 D

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(M1.MC.13.114) A 14-year-old male is brought to the Emergency Department by his mother. She is worried because his face has become puffy and his urine has turned a tea-color. Patient history reveals the child recently suffered from a sore throat. The physician suspects a bacterial infection. Which of the following describes the likely bacteria responsible? Tested Concept

QID: 101573
1

Coagulase positive

7%

(34/486)

2

Catalase positive

10%

(48/486)

3

Beta-hemolytic

73%

(355/486)

4

Bacitracin insensitive

4%

(19/486)

5

Gram negative

5%

(25/486)

M 1 D

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(M1.MC.12.189) A 53-year-old female presents with worsening shortness of breath with activity. Physical exam reveals a diastolic murmur with an opening snap. The patient’s medical history is significant for a left hip replacement 10 years ago, and she vaguely recalls an extended period of illness as a child described as several severe episodes of sore throat followed by rash, fever, and joint pains. Administration of which of the following treatments at that time would have been most effective in reducing her risk of developing cardiac disease? Tested Concept

QID: 101648
1

Acyclovir

0%

(0/42)

2

Penicillin

86%

(36/42)

3

Vancomycin

12%

(5/42)

4

Aspirin

0%

(0/42)

5

Ciprofloxacin

0%

(0/42)

M 3 E

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