抗生素和其它药物不同，不仅影响患者疾病过程，也对患者所在社区产生影响，因为使用抗生素可以导致细菌发生药物耐受，这些对抗生素耐受的细菌可能威胁患者社区民众甚至更大范围的公共健康。

抗生素曾经被比喻为四刃剑，首先通过杀菌作用治疗细菌感染，其次是通过控制细菌感染避免传染病扩散，这两类正面作用在抗生素发现时就已经被证明。

另外两类就不是正面作用，一是青霉素发现者亚历山大·弗莱明1945年在诺贝尔奖获奖演说中提出的，就是警告大家抗生素耐药可能危害公众健康，因为细菌可以通过抗生素压力筛选进化出耐受抗生素的能力。我们现在已经看到这种危害的后果十分严重，许多细菌已经出现了耐药类型，甚至出现超级细菌的问题，有可能给全体人类健康带来严重威胁。

第四种效应最近才认识到，抗生素可以通过干扰和改变人体内菌群危害健康，因为科学家已经发现，作为人体内环境的有机组成，细菌通过丰富的基因库，在维持宿主健康中发挥不可替代的作用。在人的幼年发育阶段，这种作用尤其明显，在成年人的健康维持方面的证据也越来越多。

http://science.sciencemag.org/content/352/6285/544

Anti-infectives,including antibiotics, are essentially different from all other drugs; they notonly affect the individual to whom they are given but also the entirecommunity, through selection for resistance to their own action. Thus, theiruse resides at the intersection of personal and public health. Antibiotics canbe likened to a four-edged sword against bacteria. The first two edges of theantibiotic sword were identified immediately after their discovery anddeployment in that they not only benefit an individual in treating theirinfection but also benefit the community in preventing the spread of thatinfectious agent. The third edge was already recognized by Alexander Fleming in1945 in his Nobel acceptance speech, which warned about the cost to thecommunity of antibiotic resistance that would inevitably evolve and be selectedfor during clinical practice. We have seen this cost mount up, as resistancecurtails or precludes the activities of some of our most effective drugs forclinically important infections. But the fourth edge of the antibiotic swordremained unappreciated until recently, i.e., the cost that an antibiotic exertson an individual’s own health via the collateral damage of the drug on bacteriathat normally live on or in healthy humans: our microbiota. These organisms,their genes, metabolites, and interactions with one another, as well as withtheir host collectively, represent our microbiome. Our relationship with thesesymbiotic bacteria is especially important during the early years of life, whenthe adult microbiome has not yet formed.