PKZ18 is an antibiotic that inhibits bacterial growth with minimum inhibitory concentrations of 32–64 μg/mL against most Gram-positive bacteria, acting by suppressing in vivo transcription and translation of glycyl-tRNA synthetase mRNA, selectively targeting stem I specifier loops in Gram-positive organisms, reducing T-box transcriptional read-through, disrupting codon–anticodon recognition required for tRNA binding, and demonstrating a mechanism that is refractory to conventional resistance development.