Construction of a severely attenuated mutant of Mycobacterium tuberculosis for reducing risk to laboratory workers.

The ability to construct defined deletions of Mycobacterium tuberculosis has allowed many genes involved in virulence to be identified. Deletion of nutritional genes leads to varying levels of attenuation, presumably reflecting the need for a particular molecule, and the availability (or lack) of that molecule in vivo. We have previously shown that M. tuberculosis mutants lacking either the trpD or ino1 gene are highly attenuated in mouse models of infection, but can grow when supplemented with tryptophan or inositol, respectively. In this paper we have constructed a double Delta trpDDelta ino1 mutant, and show that this is severely attenuated in SCID mouse and guinea pig models. As the strain will grow in the presence of supplements, we propose that this strain could be used for research and antigen preparative purposes, with reduced risks to laboratory workers.