Since lung puncture is an invasive method, it cannot be used in routine diagnosis. Almost all cases of pneumonia, however, can be detected by simple clinical signs, without radiography or laboratory data. Pathogenesis of Bacterial Pneumonia Infectious agents enter the lower respiratory tract by hematogenous spread or by inhalation or aspiration into the tracheobronchial tree. Metastatic pneumonias from right-sided endocarditis or from septic thrombophlebitis are well documented. Hematogenous spread appears to be an important mechanism for E. coli pneumonia too.
Meningococcal pneumonia is usually secondary to meningococcemia in children.
Unlike viruses, airborne transmission of bacteria is uncommon, except for tuberculosis. Aspiration of potentially pathogenic bacteria from the oropharynx is the most frequently implicated mechanism of bacterial pneumonia. Several host defense mechanisms account for pulmonary protection from various infectious agents. Balance of defense mechanisms and bacterial factors. The upper airway passages are capable of filtering and trapping pathogens by means of the mucociliary system and the cough reflex.