The Importance of Obligate Anaerobes and the Streptococcus anginosus Group in Pulmonary Abscess: A Clone Library Analysis Using Bronchoalveolar Lavage Fluid

Background: Appropriate antibiotic use reduces the mortality of patients with lung abscess; however, 40-60% of the bacterial etiologies in these patients have remained unknown with the culture methods. Obligate anaerobes and the Streptococcus anginosus group are common pathogens in lung abscess, but a precise evaluation of these bacteria by ordinary culture methods seems to be difficult due to upper respiratory tract contamination. Objectives: The aim of this study was to assess the microbiota of lung abscess by bronchoalveolar lavage fluid (BALF) using the molecular method in comparison to culture methods. Methods: BALF samples obtained from the affected lesions and sputum samples of 59 patients with lung abscess were evaluated. The microbiota in BALF was analyzed according to the molecular method using the 16S ribosomal RNA gene. Results: Fifty-six of the 59 BALF samples were positive in polymerase chain reaction analysis. Fusobacterium spp. (23.7%) were most frequently detected, followed by the S. anginosus group (15.3%), as the predominant phylotypes. Obligate anaerobes were detected in 42.4% of the BALF specimens as the predominant phylotypes, whereas the detection rate of obligate anaerobes was 13.6% by culture methods using BALF. In addition, the detection rate among those patients in whom the phylotype of obligate anaerobes was detected in >5% of the lung microbiota according to the molecular method was 86.5% in the 'mixed-bacterial' infection group. Conclusions: The findings by the molecular method suggest that obligate anaerobes play important roles in the pathogenesis of lung abscess and provide additional bacterial information regarding conventional culture methods.
Respiration

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