The most common bacteria causing bacterial lobar pneumonia is -

Correct option is B

Ans. (b) Streptococcus pneumoniae
Explanation:
Lobar pneumonia is a type of community-acquired pneumonia (CAP) that involves inflammation and consolidation of an entire lobe of the lung. The most common bacterial cause is Streptococcus pneumoniae (pneumococcus).
Why is Streptococcus pneumoniae the most common cause?
1. High Virulence:
· Capsulated bacterium that evades immune defenses.
2. Primary Invader in Immunocompromised Hosts:
· Often infects individuals with weakened immunity (elderly, children, chronic lung disease, smokers, diabetics).
3. Classic Symptoms of Lobar Pneumonia:
· High fever with chills
· Rust-colored sputum (due to alveolar hemorrhage)
· Pleuritic chest pain
· Cough with purulent sputum
· Lung consolidation (seen on chest X-ray as a single affected lobe)
Why are the other options incorrect?
1. Staphylococcus aureus → (Incorrect Choice)
· Causes bronchopneumonia (patchy infiltrates), not lobar pneumonia.
· More common in hospital-acquired pneumonia (HAP) and post-viral infections (e.g., after influenza).
2. E. coli → (Incorrect Choice)
· Causes hospital-acquired pneumonia (HAP), especially in ventilator-associated pneumonia (VAP).
· Rare in community-acquired lobar pneumonia.
3. Pseudomonas aeruginosa → (Incorrect Choice)
· A common cause of pneumonia in hospitalized and immunocompromised patients (e.g., cystic fibrosis, ventilator-associated pneumonia, or burn patients).
· Causes diffuse bronchopneumonia, not classical lobar pneumonia.