Background: Mycoplasma mycoides subsp mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP), a disease mainly characterized by pneumonia and pleural effusion. Though pleural fluid (PLF) samples could be used for isolation of Mmm from infected animals, proteomics of bovine PLF and in vivo produced Mmm from the natural host have not been characterized so far. Objectives: Proteomic characterization of bovine PLF and in vivo grown Mmm from cattle with CBPP Methods and results: Pleural effusions from seven experimentally infected cattle with pathogenic Mmm were analyzed. Viable Mmm cells up to 108 cells mL-1 were present in the PLF. Protein gel electrophoresis and mass spectrometry of PLF samples revealed 963 bovine proteins. When compared with plasma proteome, significant numbers of physiological plasma proteins were detected. In addition, acute phase proteins (APP) were highly abundant in PLF compared to plasma. With regards to Mmm, proteomic analysis revealed 315 in vivo produced Mmm proteins. Based on comparison with respective data banks, these proteins could be assigned to capsule synthesis, hydrogen peroxide production and induction of inflammatory response. Conclusions: The high number of viable Mmm points towards bovine pleural effusion as the "in vivo niche" of Mmm consisting of proteins, which are comparable to protein composition of bovine plasma, but with abundant APPs. Presumably, in vivo produced Mmm proteins are important for Mmm survival in the host. These Mmm proteins could be used for comparison with in vitro studies to better understand underlying pathogenicity and identify potential vaccine targets. (Texte intégral)