**Pneumonia** (lung infection) is caused most commonly by which bacterium?
A*Salmonella typhi* (typhoid)
B*Streptococcus pneumoniae* (also *Haemophilus influenzae*); causes alveoli to fill with pus → impaired gas exchange
C*Mycobacterium tuberculosis* (TB, distinct disease)
D*Escherichia coli*
Answer & Solution
Correct answer: B. *Streptococcus pneumoniae* (also *Haemophilus influenzae*); causes alveoli to fill with pus → impaired gas exchange
Bacterial pneumonia: *Streptococcus pneumoniae* (~most common), *Haemophilus influenzae*, *Mycoplasma pneumoniae* (atypical), *Legionella*. Viral pneumonia: influenza, RSV, SARS-CoV-2. Alveoli fill with fluid/pus → consolidation visible on X-ray, productive cough, hypoxia. Vaccines (pneumococcal) available.
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