STREPTOCOCCI

STREPTOCOCCI

1. Definition:

• Streptococci are a group of Gram-positive cocci
• They are catalase-negative
• They are facultative anaerobes

2. Types of Streptococci:

• Alpha-hemolytic streptococci: e.g. Streptococcus pneumoniae
• Beta-hemolytic streptococci: e.g. Streptococcus pyogenes
• Gamma-hemolytic streptococci: e.g. Streptococcus viridans

3. Streptococcus Pyogenes:

• Also known as Group A beta-hemolytic streptococci (GABHS)
• It is the most common cause of pharyngitis and impetigo in humans

4. Morphology of Streptococcus Pyogenes: → Streptococcus pyogenes is a Gram-positive, catalase-negative, facultative anaerobe → It is a chain-forming coccus → It has a diameter of 0.5-1.0 microns

5. Virulence Factors of Streptococcus Pyogenes:

• M protein: a surface protein that prevents phagocytosis
• C-carbohydrate protein: an adhesin that helps the bacteria to adhere to host cells
• Pyrogenic exotoxins: exotoxins that cause fever and inflammation
• Hyaluronic acid: a polysaccharide that is involved in the production of a biofilm

6. Pathogenicity of Streptococcus Pyogenes:

• Streptococcus pyogenes causes a range of diseases including pharyngitis, impetigo, cellulitis, and rheumatic fever
• It invades the host cells by adhering to the host cells using the C-carbohydrate protein
• The bacteria then produce pyrogenic exotoxins that cause fever and inflammation
• The bacteria can also produce hyaluronic acid that helps to form a biofilm that protects the bacteria from the host's immune system

7. Pathogenesis of Post-Streptococcal Sequelae:

• Rheumatic fever: occurs when the host's immune system reacts to the presence of Streptococcus pyogenes
• Acute glomerulonephritis: occurs when the host's immune system reacts to the presence of Streptococcus pyogenes
• Acute rheumatic carditis: occurs when the host's immune system reacts to the presence of Streptococcus pyogenes

8. Laboratory Diagnosis of Streptococcal Infections:

• Culture and isolation of the bacteria from a throat swab or skin lesion
• Identification of the bacteria using Gram staining and biochemical tests
• Serological tests: such as the rapid streptococcal test (RST) and the latex agglutination test (LAT)
• Molecular tests: such as PCR and DNA sequencing