Most common causative organism for lobar pneumonia is –
## **Core Concept**
Lobar pneumonia is a type of pneumonia characterized by an acute inflammatory process that affects one or more lobes of the lungs. It is often caused by bacterial infections. The most common causative organism for lobar pneumonia is a type of bacterium that is commonly found in the respiratory tract.
## **Why the Correct Answer is Right**
The correct answer, *Streptococcus pneumoniae*, is the most common cause of lobar pneumonia, accounting for approximately 80% of cases. This bacterium is a gram-positive coccus that can colonize the respiratory tract and cause disease under certain conditions. *S. pneumoniae* produces virulence factors such as a polysaccharide capsule that helps it evade the host immune system.
## **Why Each Wrong Option is Incorrect**
* **Option A:** *Klebsiella pneumoniae* is a gram-negative rod that can cause pneumonia, particularly in hospitalized patients or those with underlying health conditions. While it is a significant cause of pneumonia, it is not the most common cause of lobar pneumonia.
* **Option B:** *Haemophilus influenzae* is a gram-negative coccobacillus that can cause pneumonia, especially in children. However, it is not the most common cause of lobar pneumonia in adults.
* **Option D:** *Pseudomonas aeruginosa* is a gram-negative rod that can cause pneumonia, particularly in immunocompromised individuals or those with cystic fibrosis. It is not typically associated with lobar pneumonia in otherwise healthy individuals.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that *Streptococcus pneumoniae* is a common cause of community-acquired pneumonia (CAP), and lobar pneumonia is a classic presentation of CAP. The pneumococcus vaccine is available to prevent infections caused by *S. pneumoniae*, particularly in high-risk populations.
## **Correct Answer:** . Streptococcus pneumoniae