The infecting bacteria of acute lung abscess are common bacteria in the upper respiratory tract and oral cavity. It is often a mixed infection, including aerobic and anaerobic Gram-positive and -negative cocci and bacilli. Among them, the most common pathogens are Staphylococci, Streptococci, Pneumococci, Fusobacteria and spirochetes. The importance of anaerobic bacteria to purulent pulmonary infections has only been recognized in recent years due to the improvement of culture technology. The more important anaerobic bacteria include Streptococcus pneumophila, Peptococcus pneumoniae, Fusobacterium nucleatum, Bacteroides, Varroa, and spirochetes. In addition to the above-mentioned anaerobic bacteria, there are also aerobic or facultative anaerobic bacteria. In recent years, foreign reports have shown that about 25% of pneumonia caused by Legionella pneumophila forms abscesses