Actinomycetes are ubiquitous bacteria and some can be potentially pathogen for Humans in the air of some working areas. It’s notably the case in composting plants where bacteria concentrations can reach high values. Workers exposure to these inhalable bioaerosols can be source of various diseases (hypersensitivity pneumonitis notably). Although this problem is admitted, bibliography reveals a lack of knowledge about risk assessment: currently, none global method for bioaerosols sampling and analysis is standardized. So much that neither dose-effects relationship for most of these bacteria, nor Threshold Limit Value exists. Traditional methods, that are used, have some drawbacks (concentrations underestimation notably) and most often, aren’t specific.It’s the reason why the aim of the thesis, here described, is the development and the evaluation of the biomolecular technique of real time PCR for the quantification of bacteria in these bioaerosols. First, this method was developed and improved by oligonucleotides design, by comparison of many DNA extraction protocols and by the construction of standard ranges. Then, the method was compared to traditional widely used methods such as cultivable bacteria counting by cultures and epifluorescence microscopy, both on cells culture samples and experimental bioaerosols. After this characterization, the analytic method was applied on environmental bioaerosols sampled on real exposure conditions (composting plants).The method that we have developed, based on DNA extraction and real-time PCR, allows the quantification of Thermoactinomyces vulgaris DNA (based on gyrB gene amplification), of Thermobifida fusca and T. alba (ecf gene) and of mesophilic streptomycetes (rDNA 23S). The results obtained by PCR are strongly correlated with those obtained by counting on agar but PCR method offers more advantages than cultures. As PCR quantifies any form of the bacteria (vegetative cells and spores), the method goes over the drawbacks of traditional methods, like underestimation. The method has a real advantage of specificity, it’s also repeatable and sensitive. Sampling campaigns realized on 5 composting plants implanted in France have permitted measuring mesophilic and thermophilic bacteria concentrations by culture and establishing Thermoactinomyces vulgaris, Thermobifida sp. and Streptomyces sp. ones by PCR. The study confirms that composting activities release bioaerosols. And according to the localization of the sampling, the values could be rather high. It also underlines some informations as particles size distribution of the bioaerosol or the adequacy between sampling apparatus and PCR analysis. The works carried out, from qPCR method development for actinomycetes group to its application on environmental samples, give a lot of datas concerning airborne actinomycetes quantification. It permit to validate the developed method and give the only currently available measures for T. vulgaris, Thermobifida sp., and mesophilic streptomycetes in the air of composting plants
