Isolation of RNA from mycobacteria grown under in vitro and in vivo conditions

Isolation of RNA from mycobacteria is very difficult to perform, and the yields are generally very low. We describe an approach to isolate RNA from mycobacterial species which combines the disruption of mycobacterial cells by a silica/ceramic matrix in a reciprocal shaker with the ease and efficiency of subsequent RNA purification on spin columns with silica gel-based membranes. This method is rapid, easy to perform and yields high amounts of pure, intact total RNA. Due to its safety, this method is applicable even to group 3 biological hazard organisms like Mycobacterium tuberculosis. By combining a method for the isolation of phagosomal bacteria from infected primary macrophages with the novel RNA isolation technique, we are able to monitor gene expression during infection even in bacteria which are rather resistant to genetic manipulation, like Mycobacterium bovis.