Streptococcus pyogenes (Group A Streptococci) - Microbiology

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

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

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