High-ionic strength interference of ribosomal inhibition produced by aminoglycoside antibiotics.

A protein synthesis cell-free system capable of performing with similar efficiencies in different ionic conditions has been developed for the halotolerant marine bacterium Vibrio costicola. The system has been used to test the effect of ionic strength on the interference produced by thirty translation inhibitors with different structural, functional, and domain specificities. In general, at high ionic strengths, the inhibition of protein synthesis produced by polycationic antibiotics like the aminoglycosides is much less pronounced than the inhibition obtained at low ionic strengths, while non-aminoglycosidic antibiotics show similar inhibitory activities at both high and low ionic conditions. These results strongly suggest that competition between polycationic antibiotics and cations at high concentrations in the media is responsible for the lack of inhibition by aminoglycoside antibiotics at high ionic strengths, rather than a lack of binding sites.