Microorganisms associated with plants may alter the traits of the human microbiome important for human health, but this alteration has largely been overlooked. The plant microbiome is an interface between plants and the environment, and provides many ecosystem functions such as improving nutrient uptake and protecting against biotic and abiotic stress. The plant microbiome also represents a major pathway by which humans are exposed to microbes and genes consumed with food, such as pathogenic bacteria, antibiotic-resistant bacteria, and antibiotic-resistance genes. In this review we highlight the main findings on the composition and function of the plant microbiome, and underline the potential of plant microbiomes in the dissemination of antibiotic resistance via food consumption or direct contact.

Schematic Overview of the Plant Microbiome. The aboveground components of plants, collectively known as the phyllosphere, represent an inherently open and variable habitat dominated by leaves. Antibiotic resistomes associated with phyllospheres can influence human microbiomes by direct consumption and contact, or through the food chain. The belowground components of plants, especially the narrow zone of soil surrounding the plant roots, are collectively known as the rhizosphere, which contains many microbes. The rhizospheric microbiome provides the plant with nutrient acquisition, tolerance to abiotic stress, and protection against viruses and other pathogens via induced systemic resistance (ISR) and activation of the plant immune system in response to foliar pathogenic attack (immune response). The rhizospheric microbiome, however, also facilitates the spread of antibiotic resistomes and puts human health at risk from contaminated food.