Pneumonia results from the proliferation of microbial pathogens at the level of:

Pneumonia results from the proliferation of microbial pathogens at the alveolar level. The most common way of access is by aspiration from the oropharynx Rarely, pneumonia occurs hematogenous spread (e.g., from tricuspid endocarditis) or by contiguous extension from an infected pleural or mediastinal space. Ref: Harrison, E-18, P-2131