Most common causative organism for lobar pneumonia is

Streptococcus pneumoniae are the most common cause of pneumonia, both lobar and bronchopneumonia. The aspiration of nasopharyngeal secretion containing Streptococcus pneumoniae into the lower respiratory tract is a common event and may occur even in sleep. Normal mucosal defense mechanisms such as entrapment, expulsion and cough reflex, aided by the ciliary escalator effect, prevent the establishment of infection. When the normal defenses are compromised by a viral infection, anesthesia, chilling and other factors, Streptococcus pneumoniae penetrate the bronchial mucosa and spread through the lung along with the peribronchial tissues and lymphatics. Bacteremia is common during the early stage. Toxemia is due to the diffusion of the capsular polysaccharide into blood and tissues. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 226