Key Words Normal flora √正常菌群 Opportunistic pathogen√条件致病菌 Normal microbiota Opportunistic infection√机会感染 Nosocomial infection 医院感染 Microeubiosis 微生态平衡 microdysbiosis 微生态失衡/失调 Friends or Foe?Key Words Normal flora Opportunistic pathogen Normal microbiota Opportunistic infection Nosocomial infection Microeubiosis microdysbiosis  正常菌群  条件致病菌  机会感染  医院感染  微生态平衡  微生态失衡/失调 Friends or Foe?