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The present invention is directed to D-alanine racemase mutants of mycobacterial species. The D-alanine racemase gene (alrA) is involved in the systhesis of D-alanine, a basic component of peptidoglycan that forms the backbone of the bacterial cell wall. The vresent invention is also directed to methods of making live-attenuated vaccines against pathogenic mycobacteria using such alrA mutants and to the vaccines made according to such methods. The present invention is further directed to use of alrA mutants in methods for screening antimycobacterial agents that are synergistic with peptidoglycan inhibitors. Finally, the present invention is directed to methods to identify new pathways of D-alanine biosynthesis for use in developing new drugs targeting peptidoglycan biosynthesis in mycobacteria and to identify vaccines useful against pathogenic mycobacteria.