Updated: 11/14/2018

Streptococcus pyogenes (Group A Streptococci)

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Introduction

  • Classification 
    • bacteria 
      • Gram-positive cocci
        • Streptococcus
          • S. pyogenes (Group A strep, or "GAS") 
  • Pathogenesis
    • transmission
      • direct contact
      • respiratory
    • reservoir
      • throat
      • skin
    • molecular biology
      • M protein
        • main virulence factor
        • inhibits phagocytosis 
        • inhibits complement activation
        • mediates bacterial attachment
        • antigenic
          • antibodies to M protein can give rise to rheumatic fever 
      • hyaluronic acid capsule
        • non-immunogenic
      • streptolysin O
        • immunogenic
        • lyses erythrocytes and PMNs
        • ASO titer reveals the presence of this antigen
      • streptolysin S
        • non-immunogenic
      • streptokinase
        • dissolves clot
      • hyaluronidase
        • dissolves connective tissues
      • erythrogenic toxin (SPE-A)
      • anti-DNase
        • antibody
        • stays elevated for longer - useful for diagnosis
Presentation
  • GAS is pyogenic, toxigenic, and immunogenicStrawberry tongue
    • pyogenic pharyngitis
        • acute onset sore throat, fever, malaise, and headache
        • "exudative tonsillitis"
          • however, 70% of exudative tonsilitis is caused by viruses
          • don't assume GAS solely based on finding of exudative tonsilitis
        • tonsillar abscesses
        • tender anterior cervical lymph nodes
      • cellulitis
      • impetigo 
        • honey-crusted lesions
    • toxigenic
      • scarlet fever 
      • sandpaper rash sparing palms and soles
      • strawberry tongue 
      • toxic shock syndrome
    • immunogenic
      • rheumatic fever
        • antibodies to heart tissue 
        • type II hypersensitivity
        • symptoms include
          • subcutaneous plaques
          • polyarthritis
          • erythema marginatum
          • chorea
          • carditis
        • occurs following pharyngitis
        • does NOT occur following skin infection (impetigo) 
      • post-streptococcal glomerulonephritis (PSGN) 
        • immune deposits in glomeruli
        • type III hypersensitivity
        • associated with M12 serotype
        • occurs following either pharyngitis or impetigo
    • "PHaryngitis can result in rheumatic PHever and nePHritis"
Studies
  • Diagnosis
    • rapid strep test is ELISA based
      • misses 25% of infections → culture all negative tests
    • ASO (anti-streptolysin O) titer detects recent infection
      • >200 indicates rheumatic fever
  • Evaluation
    • bacitracin sensitive
    • β-hemolytic
    • PYR (pyrrolidonyl arylamidase) positive
Treatment
  • Pharmacologic
    • beta-lactam medications
      • penicillin derivatives
      • cephalosporins
    • macrolides if penicillin allergy
    • consider prophylactic antibiotics post acute rheumatic fever
    • prompt treatment prevents rheumatic fever 
      • but does NOT affect likelihood of developing post-streptococcal glomerulonephritis
 

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Questions (9)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.MC.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? Review Topic

QID: 101648
1

Acyclovir

0%

(0/22)

2

Penicillin

86%

(19/22)

3

Vancomycin

9%

(2/22)

4

Aspirin

0%

(0/22)

5

Ciprofloxacin

0%

(0/22)

M1

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PREFERRED RESPONSE 2
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(M1.MC.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? Review Topic

QID: 101616
1

M protein

69%

(24/35)

2

Streptolysin O

20%

(7/35)

3

Streptolysin S

0%

(0/35)

4

Pyrogenic toxin

0%

(0/35)

5

Streptokinase

6%

(2/35)

M1

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PREFERRED RESPONSE 1

(M1.MC.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? Review Topic

QID: 101611
FIGURES:
1

Type III hypersensitivity reaction

43%

(3/7)

2

Coagulase activity

0%

(0/7)

3

Leukocidin activity

0%

(0/7)

4

Type I hypersensitivty reaction

0%

(0/7)

5

Molecular mimicry

57%

(4/7)

M1

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PREFERRED RESPONSE 5
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(M1.MC.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? Review Topic

QID: 101573
1

Coagulase positive

7%

(34/464)

2

Catalase positive

10%

(46/464)

3

Beta-hemolytic

72%

(335/464)

4

Bacitracin insensitive

4%

(19/464)

5

Gram negative

5%

(25/464)

M1

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PREFERRED RESPONSE 3

(M1.MC.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? Review Topic

QID: 101474
FIGURES:
1

Sporothrix schenckii

14%

(2/14)

2

Staphylococcus aureus

0%

(0/14)

3

Streptococcus mutans

7%

(1/14)

4

Staphylococcus epidermidis

0%

(0/14)

5

Streptococcus pyogenes

71%

(10/14)

M1

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PREFERRED RESPONSE 5
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