The purified Pseudomonas aeruginosa cell wall biosynthesis MurD amide ligase enzyme was used to screen C-7-C and 12 mers peptides from phage display libraries using competitive biopanning approaches with the specific substrates D-glutamate and ATP. From the 60 phage-encoded peptides identified, DNA was sequenced, deduced amino acid sequences aligned and two peptides were synthesized from consensus sequences identified. The UDP-N-acetylmuramyl-L-alanine MurD substrate was synthesized, purified and used to develop a spectrophotometric assay. One peptide synthesized was found to specifically inhibit ATPase activity of MurD. The IC50 value was estimated at 4 microM for the C-7-C MurDp1 peptide. The loop conformation of MurDp1 was shown to be important for the inhibition of the UDP-N-acetylmuramyl-L-alanine:D-glutamate MurD ligase. The linear 12 mers MurD2 peptide has an IC50 value of 15 mM. A conserved amino acid motif was found between MurDp2 and the bacterial glyceraldehyde 3-phosphate dehydrogenase indicating that MurDp2 binds at a protein-protein interacting site. The approach proposed and results obtained suggest that efficient peptide inhibitors as well as protein-protein interaction domains can be identified by phage display.