The present invention allows a screening method for identifying novel drugs for the treatment of tuberculosis as well as a diagnostic method for identifying clinical strains that are resistant to these novel drugs. In particular, the present invention relates to a method for screening in vitro drug candidates for the treatment of tuberculosis by interfering with the arabinogalactan biosynthesis, the said method comprising a step of putting into contact a Mycobacterium tuberculosis cell culture over-expressing a protein that performs the transformation of decaprenyl-P-ribose to decaprenyl-P-arabinose and that can be encoded by rv3790 gene or homologues thereof or any open-reading artificial frame whose gene product is identical or homologue to Rv3790 protein, with a drug candidate and then evaluating the percentage of inhibition caused by the drug candidate against a control in an assay test, such as an antibacterial test or an enzymatic test.