Feglymycin is a 13-amino acid peptide originally isolated from Streptomyces that has antibacterial and antiviral activities. It is active against Gram-positive bacteria (MICs = 32-64 µg/ml) and inhibits HIV viral replication in H9 cells (IC50 = ~5 µM). Feglymycin is also active against clinical isolates of HIV-1 from clades A-D, A/E, and G (EC50s = 0.5-6.7 µM). It interacts with gp120 and inhibits HIV-1 NL4.3 binding to human soluble CD4 (EC50 = 4.4 µM) and to CD4+ SupT1 T cells by 74.5% when used at a concentration of 10.5 µM. Feglymycin inhibits the E. coli peptidoglycan biosynthesis enzymes MurA and MurC (Kis = 3.4 and 0.3 µM, respectively) in a noncompetitive manner.