Medicoapps masterclass on Streptococcus pyogenes

1. Streptococcus pyogenes
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#Masterclass
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S pyogenes – Morphology & Cultural Characterstics
Morphology Cultural Characteristics
Requires media with fermentable carbohydrate / serum / blood
Growth and Hemolysis promoted by 10% CO2
Gram (+) ChainsGroup A
Capsulated Form are Virulent (Produce Matt or Mucoid Colony)
Non capsulated form are avirulent (Produce Glossy Colony)
Biochemical Characteristics
Bacitracin Sensitive
PYR Positive
CAMP (-)Catalase (-)
Ribose Not Fermented

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S pyogenes – Antigenic Structure
Antigenic Structure
Hair Like Pilla (Fimbria)
For attachment to epithelial cells
Cell Wall
Inner Layer Peptidoglycan
Middle Layer Carbohydrate (Lancefield Classification)
Outer Layer Proteins & Lipoteochoic Acid ( M Protein , T and R )
M Protein (Griffith) - Virulence (Inhibits Phagocytosis)
Antibodies Against M Protein is protective
T and R have no relation to Virulence
Polysaccharide Capsule
Imp in protection from phagocytosis
GAS* Colonization in pharynx (CD - 44)
Weak Immunogen ( Ab not Protective)
*GAS – Group A Streptococci

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Antigenic Similarity
Streptococcus pyogenes Human Cells
Capsular Hyaluronic acid Synovial Fluid
Outer Cell Wall - Protein Myocardium
Middle Wall - (A) Carbohydrate Cardiac Valves
Inner Cell Wall Skin Antigen
Cell Membrane Vascular Intima

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Toxins & Virulence Factors
Hemolysin - Streptolysin
Two Types:- Oxygen Labile (O) and Oxygen Stable or Serum Soluble (S)
ASO Titre (Anti Streptolysin O Titre) - Retrospective Diagnosis (>200)
Pyrogenic Exotoxin/ Dick / Scarlatinal
Also called Erythrogenic (Superantigen causing TSS
Dick Test – I/D Test to Identify susceptible children (Schultz Charlton Rn
Type A (M/C) and Type B – Bacteriophage Type C - Chromosome
Streptokinase (Fibrinolysin) Facilitates Spread of Infection. Produced by Serotype A, C & K
Deoxyribonuclease (Streptodornase) Thin Serous character of Strep Exudates
Spy Lep Serine Protease – Cleave / Inactivated IL-8 (Inhibit Neutrophil Recruitment)
Hyaluronidase Favor Spread of Infection
Serum Opacity Factor Lipoproteinase
Nicotinamide Adenine Dinucleotidase (NADase )
Oxygen Labile [O] Oxygen Stable [S]
Antigen Specific Non Antigenic (S)
Activity on Pour Plate Hemolysis on Surface(S)
Cardiotoxic Non Cardiotoxic (S)

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Clinical Manifestations
Respiratory
Sore Throat is the M/C Streptococcal Infection
Scarlet Fever
Streptococcal Pharyngitis + Rash with Minute Papules (Sand Paper Skin)
Associated with Circumoral palor + Strawberry Tounge
Sandpaper Skin Circumoral Palor Strawberry Tounge

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Skin / Soft Tissue
Cellulitis – M/C by St Pyogenes (Also – Staph , Cl. Perfringes and E Coli
Erysipelas – Superficial Form of Cellulitis esp on Cheeks ( Peau- d orange Texture due to Lymphatic involvement
Necrotizing Fascitis – Group A Streptococci . Called Hemolytic Streptococci Gangrene
In Skin Infections ASO Titres are not High , so estimation not of any significance
Clinical Manifestations
Impetigo – Mainly by Group A Streptococci M/C on Face & Legs
Non Bullous
Impetigo
Bullous Impetigo Cellulitis Erysipelas
Necrotizing
Fascitis

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Clinical Manifestations
Genital Infections
Anaerobic Streptococci are most important cause of puerperal sepsis
Bacteremia
Bacteremia , Pneumonia and Toxic Shock Syndrome
Non Suppurative Complications 1-3 Weeks after Infection
Acute Rheumatic Fever Acute Glomerulonephritis
Post Throat Infection (Any Serotype) Skin / Throat Serotypes 49, 53-55, 59-64, 1 & 12
Repeated Attacks Common Not Seen
Penicillin Prophylaxis Indicated Not Indicated
Course – Progressive / Static Self Limiting
ASO Titre Raised May or May not (Skin Infection) Raised
Marked Immune Response No Change in Complement Moderate Immune Response with ↓ Complement Level

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Lab Diagnosis & Treatment
Lab Diagnosis
Acute Pharyngitis – Swab Culture (Gold Standard)
Transport Media – Pike’s Media
Sheep Blood Agar recommended (As it is inhibitory to H. hemolyticus)
ARF and Ac GN retroscpective with ↑ ASO Titres ( ASO > 200)
In Ac GN & Pyoderma Anti DNAse and Antihyaluronidase used for retrospective diagnosis
Streptozyme Test :- Passive Haemagglutination Test (Specific and Sensitive for all Streptococcal Infections)
Management
Penicillin :- Pharyngitis / Impetigo / Erypsipelas / Cellulitis
Penicillin + Clindamycin + Surgical Debridement :-Necrotizing Fascitis / Myositis
Penicillin + Clindamycin + i/v Ig :- Streptococcal TSS
Penicillin + Empyema Drainage:-Empyema or Pnemonia