Streptococci Classification and Characteristics

What is the suspected diagnosis of the first case based on the physical examination and laboratory results?

What is the likely cause of the patient's symptoms in the second case?

What is the purpose of performing a RADT (Rapid Antigen Detection Test) in the first case?

What is the significance of the patient's history of repetitive attacks of acute follicular tonsillitis in the second case?

What is the likely diagnosis of the second case based on the patient's symptoms and laboratory results?

What is the purpose of performing a microscopical examination of the patient's throat or tonsillar region in the first case?

What is the significance of the patient's ECG and Echo results in the second case?

What is the likely cause of the patient's elevated CRP and ESR in the first case?

What is the purpose of performing a culture on blood agar in the first case?

What is the proper management of the second case?

Streptococci

Gram-positive cocci, arranged in chains (except S. pneumoniae, which is arranged in pairs)
Non-capsulated (except S. pneumoniae and a few other exceptions)
Non-motile, non-spore forming, and fastidious organisms

Classification of Streptococci

Facultative anaerobes
Alpha-hemolytic: partial hemolysis (e.g., viridans streptococci, S. pneumoniae)
Beta-hemolytic: complete hemolysis (e.g., S. pyogenes)
Gamma-hemolytic: no hemolysis (e.g., S. faecalis)

Alpha-Hemolytic Streptococci

S. pneumoniae (Pneumococci)
Viridans streptococci (opportunistic pathogens of low virulence)
- S. mitis group
- S. mutans group
- S. bovis group

Streptococcus pneumoniae (Pneumococci)

Polysaccharide capsule is an important virulence factor
Alpha-hemolytic on blood agar
Optochin sensitive
Causes lobar pneumonia, meningitis, and subacute bacterial endocarditis

Beta-Hemolytic Streptococci

S. pyogenes
Causes acute follicular tonsillitis, pharyngitis, scarlet fever, acute bacterial endocarditis, and post-streptococcal diseases (e.g., acute glomerulonephritis, rheumatic fever)
Direct detection of S. pyogenes antigens from throat swabs is possible by RADT (rapid antigen detection tests)
Diagnosis:
- Microscopical examination: Gram-positive cocci, chains (non-motile, non-spore forming, non-capsulated)
- Culture characteristics: beta hemolysis on blood agar
- Antistreptolysin O Titer (ASOT): measures antibodies against streptolysin O produced by S. pyogenes

Antistreptolysin O Titer (ASOT)

Principle: streptolysin O (antigen) + RBCs + patient serum (ASO)
Positive reaction: no hemolysis
Titre: 1/highest dilution showing positive results (no hemolysis)
Diagnostic titer >200 Todd

Case Studies

Case 1: suspected diagnosis of acute follicular tonsillitis, caused by Streptococcus pyogenes
Case 2: suspected diagnosis of rheumatic fever, caused by Streptococcus pyogenes

Test your knowledge of Streptococci, a type of Gram-positive bacteria, including their classification, characteristics, and types such as alpha, beta, and gamma hemolytic Streptococci. Learn about their diagnosis, arrangement, and other important features.