Today's paper is: 

Bansal-Mutalik, R. & Nikaido, H. Mycobacterial outer membrane is a lipid bilayer and the inner membrane is unusually rich in diacyl phosphatidylinositol dimannosides. PNAS 111, 4958-4963 (2014).

The shortest-possible summary: Mycobacteria like M. tuberculosis have cell walls but they have nice, thick lipid membranes, too. All these layers add up to protection from antimicrobial compounds: the bacteria won't get killed if antimicrobials can't even get inside them.