Selection of genes of Mycobacterium tuberculosis upregulated during residence in lungs of infected mice.

In sequel to previous report [Srivastava V, Rouanet C, Srivastava R, Ramalingam B, Locht C, Srivastava BS. Macrophage-specific Mycobacterium tuberculosis genes: identification by green fluorescent protein and kanamycin resistance selection. Microbiology 2007;153:659-66], the genes of Mycobacterium tuberculosis upregulated during residence in lungs of infected mice were identified in an in vivo expression system based on kanamycin resistance. A promoter library of M. tuberculosis was constructed in a promoter trap shuttle vector pLL192 containing an artificial bicistronic operon composed of promoterless green fluorescent protein gene followed by kanamycin resistance gene. The library was introduced in M. bovis BCG and then infected in mice by intravenous route. Mice were treated twice daily with 40 mg/kg dose of kanamycin by intramuscular route for 21 days. Recombinant BCG recovered from the lungs were reinfected in mice to enrich clones surviving kanamycin treatment in the lung but sensitive to killing by kanamycin in vitro. After nucleotide sequencing of inserts from these clones, 20 genes belonging to fatty acids metabolism, membrane transport, nitric oxide defence and PE_PGRS/PPE family were identified. Real-time PCR analysis using RNA isolated from M. tuberculosis grown in vitro and from the lungs, confirmed upregulation of genes from 2 to 20-fold in vivo compared to growth in vitro. Several of these select 20 genes were also found upregulated ex vivo in macrophage-like cell line J774A.1, thus, suggesting a correlation in mycobacterial gene expression between ex vivo and in vivo conditions.