一、前言正常微生物群(Normal Microbiota)是微生物与宏生物在共同历史进化过程中形成的微生物生态系(Microecosystem)。正常微生物群包括病毒,细菌、真菌,原虫及其他微生物。这些微生物,在正常条件下,对寄主非但无害而且有益。医学微生物学在以往主要重视病原微生物的研究,而对正常微生物则统乏足够的认识。早在20世纪20年代,德国的细菌学家,就 I. INTRODUCTION Normal Microbiota is a microecosystem formed by micro-organisms and macro-organisms during their common historical evolution. Normal microorganisms include viruses, bacteria, fungi, protozoa and other microorganisms. These microorganisms, under normal conditions, are not only harmless and beneficial to the host. Medical microbiology in the past, the main emphasis on the study of pathogenic microorganisms, while the lack of adequate understanding of normal microorganisms. As early as the 1920s, Germany’s bacteriologist, on