Question

Which one of the following is the correct description of Streptococcus pneumoniae causing pneumonia?

• A. Virulent, Rough, non-capsulated
• B. Non-virulent, Rough, encapsulated
• C. Virulent, Smooth, encapsulated
• D. Non-virulent, Smooth, encapsulated

Hint:

Griffith experiment rule: S = Smooth = Capsule = Virulent; R = Rough = No capsule = Non-virulent.

Answer 1

The Correct Option is C

Concept:
Streptococcus pneumoniae exists in two forms based on the presence or absence of a capsule.

Step 1: Understand bacterial forms.
• Smooth strain (S) → Has polysaccharide capsule → Virulent
• Rough strain (R) → No capsule → Non-virulent

Step 2: Role of capsule. The capsule:
• Protects bacteria from host immune system
• Enhances pathogenicity (virulence)

Step 3: Analyze options.
• (A) Rough, non-capsulated → Non-virulent $\times$
• (B) Rough but encapsulated → Incorrect combination $\times$
• (C) Smooth, encapsulated → Virulent \checkmark
• (D) Smooth, encapsulated but non-virulent → Incorrect $\times$

Step 4: Conclusion. \[ \text{Virulent form = Smooth, encapsulated bacteria} \]