In the search for new therapeutic tools against tuberculosis and to further address the therapeutic potential of pyridine-2-thiol 1-oxide (Hmpo) metal complexes, two new octahedral [M(III)(mpo)3] complexes, with M = Ga or Bi, were synthesized and characterized in the solid state and in solution. Attempts to crystallize [Ga(III)(mpo)3] in CH2Cl2 led to single crystals of the reaction product [GaCl(mpo)2], where the gallium(III) ion is in a square basis pyramidal environment, trans-coordinated at the basis to two pyridine-2-thiolato 1-oxide anions acting as bidentate ligands through their oxygen and sulfur atoms. The biological activity of the new [M(III)(mpo)3] complexes together with that of the previously reported Fe(III) analogous compound and the pyridine-2-thiol 1-oxide sodium salt (Na mpo) was evaluated on Mycobacterium tuberculosis. The compounds showed excellent activity, both in the standard strain H37Rv ATCC 27294 (pan-susceptible) and in five clinical isolates that are resistant to the standard first-line anti-tuberculosis drugs isoniazid and rifampicin. These pyridine-2-thiol 1-oxide derivatives are promising compounds for the treatment of resistant tuberculosis.Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Gral. Flores 2124, 11800 Montevideo, Uruguay.Facultade de Ciencias Farmacêuticas, UNESP, 14801-902 Araraquara, SP, Brazil.Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and IFLP (CONICET, CCT-La Plata), C.C. 67, 1900 La Plata, Argentina.Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Gral. Flores 2124, 11800 Montevideo, Uruguay. Electronic address: dgambino@fq.edu.uy.Facultade de Ciencias Farmacêuticas, UNESP, 14801-902 Araraquara, SP, Brazil.