按照细菌生存对氧气的需要与否,可将它们分为需氧菌和厌氧菌。如果用一架显微镜来观察人体的皮肤和内腔(如肠道、气管)等粘膜,可以看到它的表面寄居着大量的微生物。厌氧菌多在深层,兼性厌氧菌(这类厌氧菌在有氧的环境也能生存)在中层,表层大多数是需氧菌。正常情况下,它们不但无害,而且在免疫、营养、生物拮抗和防癌等方面还为人体立下了大功。但一旦情况有变,如 According to the need of bacteria for oxygen or not, they can be divided into aerobic and anaerobic bacteria. If you use a microscope to observe the human body’s skin and lumen (such as the intestine, trachea) and other mucous membranes, you can see its surface with a large number of microorganisms. Anaerobic bacteria in the deep, facultative anaerobic bacteria (such anaerobic bacteria can survive in aerobic environment) in the middle, the surface most of the aerobic bacteria. Under normal circumstances, they not only harmless, but also in the immune, nutrition, biological antagonism and anti-cancer and other aspects of the human body has also made great achievements. But once the situation has changed, such as