Microbiological and clinical aspects of aspiration pneumonia.

Aspiration pneumonia is characterized by a pneumonitis in a dependent segment of the lung with typical necrosis or abscess-formation in the parenchyma. Observed aspiration or predisposition to aspiration, cavitation or abscess formation, with or without empyema fluid and isolation of distinctive micro-organisms are important clues to the diagnosis. Diagnostic procedures to collect anaerobic uncontaminated secretions are transtracheal aspiration, blood cultures, pleural fluid aspiration, fibreoptic bronchoscopic protected investigations and percutaneous transthoracic aspiration. Leading pathogens in more than 90% are anaerobic bacteria, mostly species of Bacteroides, Fusobacterium, Peptococcus and Peptostreptococcus; aerobic bacteria include Staphylococcus aureus and Gram-negative bacilli, mainly Klebsiella spp. and Pseudomonas aeruginosa. Treatment depends on bacteriological results; penicillin G and clindamycin are the most useful antibiotics against anaerobes and should be administered over a long period of time (4-12 weeks), adjusted to the clinical course of the individual patient.