The chapter discusses the role of free-living amoebae as reservoirs for various microorganisms, including bacteria, viruses, and fungi. Free-living amoebae have two developmental stages: the trophozoite, which is the active feeding form, and the cyst, a resting form. These organisms are widespread in the environment, including soil, water, and air, and can survive under harsh conditions. They are known to harbor "amoeba-resistant microorganisms" (ARB), which include bacteria, viruses, and fungi that can either survive or exit the amoebae without being destroyed. The text highlights the importance of free-living amoebae as a tool for isolating ARB, particularly through amoebal coculture and enrichment techniques. It describes the culture methods for growing ARB, such as using axenic cultures and amoebal coculture, and the challenges and limitations of these methods. The chapter also provides an overview of specific ARB, including Legionella species, which have been identified as emerging pathogens and are known to cause pneumonia. Other ARB mentioned include members of the Holosporaceae, Bradyrhizobiaceae, Pseudomonaceae, Parachlamydiaceae, Mycobacteriaceae, and Mimivirus. The text emphasizes the potential ecological and public health implications of these interactions, such as the role of free-living amoebae in the transmission and survival of pathogens. It also discusses the possibility of free-living amoebae acting as reservoirs for certain strains of bacteria, such as Pseudomonas aeruginosa and Francisella tularensis. The chapter concludes by noting the ongoing research into the mechanisms of ARB survival within amoebae and their potential impact on human health.The chapter discusses the role of free-living amoebae as reservoirs for various microorganisms, including bacteria, viruses, and fungi. Free-living amoebae have two developmental stages: the trophozoite, which is the active feeding form, and the cyst, a resting form. These organisms are widespread in the environment, including soil, water, and air, and can survive under harsh conditions. They are known to harbor "amoeba-resistant microorganisms" (ARB), which include bacteria, viruses, and fungi that can either survive or exit the amoebae without being destroyed. The text highlights the importance of free-living amoebae as a tool for isolating ARB, particularly through amoebal coculture and enrichment techniques. It describes the culture methods for growing ARB, such as using axenic cultures and amoebal coculture, and the challenges and limitations of these methods. The chapter also provides an overview of specific ARB, including Legionella species, which have been identified as emerging pathogens and are known to cause pneumonia. Other ARB mentioned include members of the Holosporaceae, Bradyrhizobiaceae, Pseudomonaceae, Parachlamydiaceae, Mycobacteriaceae, and Mimivirus. The text emphasizes the potential ecological and public health implications of these interactions, such as the role of free-living amoebae in the transmission and survival of pathogens. It also discusses the possibility of free-living amoebae acting as reservoirs for certain strains of bacteria, such as Pseudomonas aeruginosa and Francisella tularensis. The chapter concludes by noting the ongoing research into the mechanisms of ARB survival within amoebae and their potential impact on human health.