S. pyogenes, or group A streptococcus, is a gram-positive bacterium known to cause a variety of infections. It appears in chains and is capsulated. It is sensitive to bacitracin and produces positive reactions to PYR tests and negative reactions to catalase and ribose fermentation tests. It possesses M proteins and other antigens that allow it to evade the immune system. It produces various toxins and enzymes that contribute to its virulence. Common manifestations include pharyngitis, impetigo, cellulitis, erysipelas, necrotizing fasciitis, and non-suppurative complications like rheumatic fever and glomerulonephritis. Diagn

1. Streptococcus pyogenes
#Medicoapps
#Masterclass
www.medicoapps.org

2. www.medicoapps.org
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

3. www.medicoapps.org
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

4. www.medicoapps.org
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

5. www.medicoapps.org
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)

6. www.medicoapps.org
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

7. www.medicoapps.org
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

8. www.medicoapps.org
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

9. www.medicoapps.org
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