Chlamydia-related bacteria classified in the Chlamydiales order, are strictly intracellular bacteria and are able for the most to replicate in free-living amoebae. Amoebae, ubiquitous in the environment and especially in water, are very resistant to disinfection used in drinking water production. Thus, amoebae may reach easily the distribution and domestic water system, potentially sheltering amoeba-resisting bacteria including Legionella, mycobacteria and Chlamydiales. Indeed, some of these amoeba-resisting bacteria have been shown to cause respiratory infections in people inhaling contaminated water. Therefore, an environmental and clinical study was conducted to determine if Chlamydiales bacteria are also involved in respiratory infections and if a transmission through domestic drinking water could occur. First, large scale molecular and serological tools specific of Chlamydia-related bacteria were developed and then were applied on clinical samples from patients with and without pneumonia. Simultaneously, water and biofilm samples from households of the same patients were investigated using molecular and culture methods for the presence of Chlamydiales bacteria. Chlamydiales were detected in the nasopharyngeal flora from patients with and without pneumonia. However, no significant difference was observed between both groups. Conversely, serological investigations showed that antibody reactivity against members of the Criblamydiaceae was associated with pneumonia. The thesis provided very efficient tools that showed the presence of Chlamydiales in human nasopharyngeal flora as well as in the majority of the domestic drinking water. However, no transmission from domestic drinking water to human could be demonstrated. These tools will help in the future specifying the ecology and pathogenicity of the Chlamydia-re\ated bacteria and especially of the species belonging to the Criblamydiaceae family.