Survival of mice infected with Mycobacterium smegmatis containing large DNA fragments from Mycobacterium tuberculosis

Abstract

Mycobacterium smegmati is typically used as a bacterial host for cloning and expressing single genes or genomic libraries of the human pathogen Mycobacterium tuberculosis. To study virulence of M. tuberculosis, we set out to ask the question, whether a genomic library derived from M. tuberculosis H37Rv confers virulence to the non-virulent M. smegmatis. A representative library from the M. tuberculosis H37Rv genome was generated and transformed into wild-type M. smegmatis. Mice were challenged with recombinant clones by intravenous, aerogenic and intranasal infection. We were unable to detect either growth or persistence of recombinant clones in tissues of infected mice; instead, the infection was cleared. Since the concern that virulent traits might be transferred, biosafety regulations often require the handling of these experiments at Biosafety Level 3. However, we failed to find any evidence that theM. tuberculosis library confers virulence when expressed in M. smegmatis. We suggest that the results, presented here, should fundamentally alter the containment requirements for similar experiments in the future.