Causative organisms were identified by diagnostic bronchoscopy in 21 cases of respiratory infections in which the potential pathogens seemed to be anaerobic bacteria. A brush was introduced into the inflammatory foci of the lung, withdrawn, and was immediately stabbed into and spread on portable agar medium. Eighteen strains of the potential pathogens, including 9 strains of anaerobic bacteria consisting of 2 strains each of Peptococcus niger, Fusobacterium nucleatum and Bacteroides melaninogenicus, and 1 strain each of Peptostreptococcus anaerobius, Eubacterium sp. and Veillonella sp. were isolated after 48 h of aerobic and anaerobic cultures. Eight of 9 anaerobic strains except for Veillonella sp. were considered to be causative organisms. In 12 cases of pneumonia and lung abscess, 8 strains of anaerobic bacteria were recovered. On the other hand, only 1 strain of anaerobic bacterium was recovered from 9 cases with bronchogenic carcinoma. Aspiration and the presence of underlying immunocompromised disorders were confirmed, or suggested in many cases of anaerobic infections. Aerobic bacteria were isolated concurrently in 3 of 9 cases from which anaerobic bacteria were isolate. Fetid sputum, cavity formation and fluid level in the pleuropul monary space are frequently observed in cases of anaerobic infections. In our cases, such stenosis or obstruction of the airway as that found in cases of bronchogenic carcinoma was not necessarily related to anaerobic infections, and Bacteroides fragilis, highly resistant to many β-lactams, was isolated only occasionally. Thus we are of the opinion that common β-lactams, including penicillins and first-or second-generation cephems, are the first choice for anaerobic respiratory infections.
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