Enterococcus Diversity, Origins in Nature, and Gut Colonization

Enterococci have evolved over eons as highly adapted members of the gastrointestinal consortia of a wide variety of hosts—humans and other mammals, birds, reptiles and insects—but for reasons that are not entirely clear, they emerged in the 1970s as some of the leading causes of multidrug-resistant, hospital-acquired infections. The taxonomy of enterococci has changed considerably over the past ten years, and the genus now includes over forty distinct species with various habitats, tropisms, and metabolic and phenotypic characteristics. These habitats include animal hosts, as well as plants, soil and water, and man-made products, including fermented foods and dairy products. Antibiotic-resistant strains of enterococci have emerged in many of these habitats, and strains with novel resistance mechanisms are isolated with alarming regularity. As a result, the relationship between the non-therapeutic use of antibiotics and the occurrence of enterococci in various non-human habitats is of substantial interest.