Colonization by the microbiota provides one of our most effective barriers against infection by pathogenic microbes. The microbiota protects against infection by priming immune defenses, by metabolic exclusion of pathogens from their preferred niches, and through direct antimicrobial antagonism. Disruption of the microbiota, especially by antibiotics, is a major risk factor for bacterial pathogen colonization. Restoration of the microbiota through microbiota transplantation has been shown to be an effective way to reduce pathogen burden in the intestine but comes with a number of drawbacks, including the possibility of transferring other pathogens into the host, lack of standardization, and potential disruption to host metabolism. More refined methods to exploit the power of the microbiota would allow us to utilize its protective power without the drawbacks of fecal microbiota transplantation. To achieve this requires detailed understanding of which members of the microbiota protect against specific pathogens and the mechanistic basis for their effects. In this review, we will discuss the clinical and experimental evidence that has begun to reveal which members of the microbiota protect against some of the most troublesome antibiotic-resistant pathogens: Klebsiella pneumoniae, vancomycin-resistant enterococci, and Clostridioides difficile.

微生物群的定植提供了我们抵抗病原微生物感染的最有效屏障之一。微生物群通过启动免疫防御、通过代谢将病原体从其首选生态位中排除以及通过直接抗菌拮抗作用来防止感染。微生物群的破坏，尤其是抗生素的破坏，是细菌病原体定植的主要危险因素。通过微生物群移植恢复微生物群已被证明是减少肠道病原体负担的有效方法，但也有许多缺点，包括可能将其他病原体转移到宿主体内、缺乏标准化以及对宿主的潜在破坏代谢。更精细的方法来利用微生物群的力量将使我们能够利用其保护能力，而没有粪便微生物群移植的缺点。要实现这一目标，需要详细了解微生物群中的哪些成员可以抵御特定病原体及其作用的机制基础。在这篇综述中，我们将讨论临床和实验证据，这些证据已经开始揭示微生物群的哪些成员可以抵御一些最棘手的抗生素耐药病原体：肺炎克雷伯菌、耐万古霉素肠球菌和艰难梭菌。