The bacterium responsible for tuberculosis, Mycobacterium tuberculosis, is notorious for its tolerance to antibiotics. It enters a dormant phase, which, it was assumed, makes it less sensitive to drugs that target dividing bacteria. But it seems that even replicating mycobacteria can fend off antibiotics.

Within days of infecting zebrafish larvae with Mycobacterium marinum, Lalita Ramakrishnan at the University of Washington in Seattle and her colleagues found dividing drug-tolerant bacteria inside macrophages, a type of immune cell. In this environment, the mycobacteria synthesized molecular 'pumps' that expel drugs from the bacterial cell and promote its replication.

When the team treated cultured human macrophages infected with M. tuberculosis with verapamil, a pump inhibitor, drug tolerance decreased, suggesting that verapamil-like drugs might be able to shorten the current six-month-minimum treatment regimen for tuberculosis.

Cell doi:10.1016/j.cell.2011.02.022 (2011)