The risk associated to the contamination of drinking water networks by Legionella is well described. These bacteria can naturally resist to various stress, they can survive in biofilms for extended periods of time and proliferate in very high numbers by invading Free-Living Amoebae (FLA). FLA themselves can be highly resistant to disinfection treatments and can consequently protect internalized bacteria from the action of treatments. Whereas lot of data has been published concerning the interactions between Legionella and FLA in water networks, there is less data available concerning the interactions between FLA and other pathogenic or potentially pathogenic microbial species. Among emerging pathogenic species, Chlamydia-like bacteria have been associated with pneumonia and recurrent miscarriage. Compared to well described Chlamydia species, these new species present many differences including an increased capacity to survive as free organisms in the environment and an increased resistance to heat. New "giant" viruses associated to FLA have also been described. They present genotypic and phenotypic characteristics that have raised major interest among microbiologists and some of them could be associated to pneumonia. The association between FLA and mycobacteria also raises important questions. Recent studies demonstrate that selected strains of Non Tuberculous Mycobacteria (NTM) that can resist selected disinfection treatments (glutaraldehyde-based treatments) are also more resistant to antibiotic treatments and present increased capacity to survive within FLA. Furthermore, most mycobacterial species can survive within amoebal cysts that are extremely resistant to disinfection treatments. Research studies summarized in this report deal with the ecology of FLA and their resistance to disinfection treatments used for various applications. The role of FLA as place for genetic exchanges between intracellular micro-organisms is also discussed, as well as interactions between FLA and Legionella, FLA and Chlamydia-like species, FLA and new "giant" viruses, and FLA and mycobacteria.
