[Bacteriological diagnosis of tuberculosis: current hieratic classification of methods]

To assure the diagnosis of tuberculosis, one needs the observation, the isolation and the identification of the causative agent Mycobacterium tuberculosis. In this approach, the microscopic exam occurs as a fast but neither sensitive or specific test. The isolation on solid media is slow and needs more than three weeks before becoming positive. Nevertheless, it is a sensitive and specific one. The identification of the isolated strain and the study of sensitivity to antibiotic agents require an equal delay. Then, 2 months are necessary to achieve the analysis. The AIDS epidemic with the increase of opportunistic mycobacterial diseases, and the unexpected arrival of resistant Mycobacteria is creating as a difficult therapeutic problem. The cultivation in liquid media with the radiometric method (Bactec) shortens the time of culture by half. The genomic amplification assay has been hopeful because it allowed results in 2 days. However, some technical difficulties happen when the test is conducted and it is less sensitive than the isolation process. The hierarchical classification of the laboratory useful process to establish the diagnosis of tuberculosis disease remains the microscopic observation of the bacilli and their isolation. Today, the use of PCR alone does not assure the diagnosis of tuberculosis, however it may be used as a additional diagnostic test.