Streptomycin was the first antibiotic to be discovered in the aminoglycoside class and is derived from an actinobacterium of the Streptomyces genus1. It is widely used in the treatment of serious bacterial infections caused by both Gram-negative and Gram-positive bacteria, including tuberculosis, endocardial and meningeal infections and the plague. Although it is known that the primary mechanism of action of streptomycin is through inhibition of protein synthesis by binding the ribosome, the mechanism of entry to the bacterial cell is not yet clear.

Mechanosensitive channel of large conductance (MscL) is a highly conserved bacterial mechanosensitive channel that directly senses tension in the membrane2. The physiological role of MscL is that of an emergency release valve that gates upon an acute drop in the osmolarity of the environment (hypo-osmotic downshock)3. Under hypo-osmotic stress, water enters the bacterial cell causing it to swell, thus increasing tension in the membrane; MscL gates in response to this tension forming a large pore of about 30 Å4, thus allowing for the rapid release of solutes and saving the cell from lysis. Because of the large pore size, MscL gating is tightly regulated; expression of a mis-gating MscL channel, which opens at lower than normal tensions, causes slow bacterial growth or even cell death5.

Bacterial mechanosensitive channels have been proposed as ideal drug targets owing to their important role in the physiology of bacteria and the lack of identified homologues in higher organisms6. We therefore performed a high-throughput screen (HTS) searching for compounds that will inhibit bacterial growth in a MscL-dependent manner. Interestingly, among the hits we found four known antibiotics, among them the widely used aminoglycosides antibiotics streptomycin and spectinomycin.

The potency of streptomycin is dependent on MscL expression in growth and viability experiments in vivo. We also provide evidence of the direct modulation of MscL channel activity by dihydrostreptomycin in patch clamp experiments in vitro. The involvement of MscL in the pathway of streptomycin action suggests not only a novel mechanism for how this bulky and highly polar molecule obtains access to the cell at low concentrations, but also new tools to modulate the potency of already known and potential antibiotics.