Sketchy Micro: Strep pneumoniae & Viridans

Streptococcus Pneumoniae and Viridans Overview

• Both Strep pneumoniae and Strep viridans are classified as alpha-hemolytic streptococci.
• Alpha hemolysis indicates partial hemolysis with a green hue around colonies due to hemoglobin oxidation.

Strep Pneumoniae Characteristics

• Possesses a polysaccharide capsule, a critical virulence factor.
• Sensitive to optochin, distinguishing it from other streptococci.
• Exhibits a dual lancet shape, appearing as diplococci.
• Soluble in bile, which aids in its identification in laboratory settings.

Clinical Significance of Strep Pneumoniae

• Major cause of community-acquired pneumonia (CAP) and associated with the acronym MOPS:
  • Meningitis
  • Otitis Media (OM)
  • Pneumonia
  • Sinusitis
• Symptoms of CAP include rust-colored sputum and lobar pneumonia.

Virulence Factors of Strep Pneumoniae

• Key virulence components include a polysaccharide capsule and IgA protease.
• Patients with sickle cell disease have an increased susceptibility to infections caused by Strep pneumoniae.

Antibiotic Sensitivity and Prevention

• Strep pneumoniae is sensitive to macrolides (e.g., erythromycin) and third-generation cephalosporins (e.g., ceftriaxone).
• Prevention is achievable via vaccination:
  • Adult vaccine is a 23-valent polysaccharide vaccine generating T cell responses with specificity to IgM.
  • Child vaccine is a 7-valent conjugated vaccine that aims for a robust T cell response and improved IgG levels.

Strep Viridans Characteristics

• Lacks a capsule, making it structurally distinct from Strep pneumoniae.
• Exhibits resistance to optochin and is bile insoluble, distinguishing it from other groups.

Clinical Importance of Strep Viridans

• Particularly notable is Strep mutans, which is a primary contributor to dental caries.
• Can lead to subacute endocarditis, primarily affecting the mitral valve in those with prior valve damage.

Mechanism of Damage in Endocarditis

• Strep viridans adheres to platelets via dextrans, allowing attachment to fibrin located in damaged tissues.

Test your knowledge on Strep pneumoniae and Strep viridans with these flashcards. Explore key concepts such as hemolytic characteristics and virulence factors. Perfect for microbiology students looking to reinforce their learning.