Definition of anaerobic bacteria: bacteria that cannot grow on agar plates in an air environment containing 10%; carbon dioxide, and can only grow and reproduce in an anoxic environment. Currently known anaerobic bacteria are divided into 31 genera, 245 species and subspecies, with Gram-negative non-bacteriophage as the most. Main features: 1, distribution: anaerobic bacteria are widely distributed in nature and the human body, for example, the intestinal flora in low-yielding fields 99.9%; is anaerobic bacteria, while E. coli and other only 0.1%;, skin, oral cavity, upper respiratory tract, female genital tract in the normal flora, 80-90%; is anaerobic bacteria. 2, infection characteristics: no bacterium anaerobic infection without certain disease type, often resulting in local inflammation, abscesses and tissue necrosis. 3, treatment characteristics: most of the non-budding anaerobic bacteria are sensitive to penicillin, cephalosporins. But the most common bacillus fragilis can produce lactamase, can destroy penicillin and cephalosporin, in the treatment must pay attention to the choice of clindamycin. In addition, methotrexate also has good effect on anaerobic bacteria.