Pseudomonic Acid, also known as mupirocin, is an antibiotic isolated from Pseudomonas fluorescens which strongly inhibits protein and RNA synthesis. Inhibition of protein synthesis was reversed by isoleucine and Pseudomonic Acid was shown to inhibit IleRS (isoleucyl-tRNA synthetase) in vitro. Pseudomonic Acid also demonstrates weak inhibitory action on FARSL (phenylalanyl-tRNA synthetase). Efficacy against staphylococci and streptococci including multiply resistant Staphylcoccus aureus and Staphylococcus epidermidis is reported with Pseudomonic Acid.An antibiotic inhibitor of isoleucyl-tRNA synthetase