Most common causative organism for lobar pneumonia is -: (A) Staphylococcus aureus, (B) Streptococcus pyogenes, (C) Streptococcus pneumoniae, (D) Haemophilus influenzae
Answer is C. Streptococcus pneumoniae is the Most common causative organism for lobar pneumonia
Adult: MC serotype associated: Type 1-8
Children: Type 6, 14, 19, 23 are frequently associated serotypes
Most Virulent: Type 3.

Ref: Apurba Sastry’s Essentials of Medical Microbiology 1/e p233 , Ananthanarayan 9/e p222