Introductory remarks: bacterial endosymbionts or pathogens of free-living amebae1.

Free-living amebae are ubiquitous in the environment and can be isolated from a variety of habitats including water, soil, air, hospital water systems, dental units, contact lens cases, and cooling towers. The interaction of amebae with other microorganisms in their environment is varied. Bacteria are a major food source for free-living amebae. However, some bacteria have established a stable symbiotic relationship with amebae. Recent reports indicate an association of amebae with intracellular bacterial pathogens. Such amebae may serve as reservoirs for maintaining and dispersing pathogenic bacteria in the environment or as vectors of bacterial disease in humans.