Which of the following is the primary determinant of virulence in Streptococcus pneumoniae?

• A. Exotoxin production
• B. Polysaccharide capsule
• C. Flagella
• D. Lipopolysaccharide (LPS)

Answer: (B)

Verified step by step guidance

1. Understand the concept of virulence, which refers to the degree of pathogenicity or the ability of a microorganism to cause disease.
2. Review the characteristics of Streptococcus pneumoniae, a Gram-positive bacterium known to cause pneumonia and other infections.
3. Recall that Streptococcus pneumoniae does not produce exotoxins or have flagella, and as a Gram-positive bacterium, it lacks lipopolysaccharide (LPS), which is found in Gram-negative bacteria.
4. Focus on the polysaccharide capsule, which is a well-known virulence factor in Streptococcus pneumoniae because it protects the bacterium from phagocytosis by host immune cells.
5. Conclude that the polysaccharide capsule is the primary determinant of virulence in Streptococcus pneumoniae, enabling it to evade the immune system and cause disease.