There is increasing interest in the investigation of non-essential pathways including bacterial cysteine metabolism for developing antibiotic adjuvants. Within this pathway the O-acetyl-ʟ-serine sulfhydrylase (OASS) enzymes CysK and CysM have been a focus. As such, the OASS enzyme of Staphylococcus aureus , Sa CysK, gained our interest. Previous efforts to inhibit CysK enzymes have mimicked the interaction between CysK and the C-terminus of serine acetyltransferase (CysE) which occurs inside the CysK active site and inhibits OASS activity. CysE peptides have only moderate potency, typically binding with micromolar affinity. In S. aureus another complex forms between Sa CysK and a transcriptional regulator CymR, but the ability of CymR peptides to inhibit CysK enzymes has not been investigated. We noticed there is variation between the C-terminus of CysE and CymR, suggesting that CymR peptides make distinct interactions with Sa CysK and may be superior inhibitors. Here we characterized CysE and CymR peptides as Sa CysK inhibitors. We found CymR peptides make more extensive molecular interactions with Sa CysK and bind with higher affinity, being the most potent peptide inhibitors of a CysK enzyme to date. A CymR pentapeptide is the minimal length required for this potency and provides a promising scaffold for developing antibiotic adjuvants targeting Sa CysK.