CAP 3 is a cholic acid-peptide conjugate (CAP) with antibacterial activity. It is active against the Gram-negative bacteria E. coli, K. pneumoniae, and A. baumanii (MIC99s = 8, 16, and 16 μM, respectively). CAP 3 increases the fluidity of model Gram-negative bacterial membranes and binds to LPS in vitro. It reduces the biomass and number of colony-forming units in E. coli biofilms in a concentration-dependent manner. CAP 3 inhibits E. coli biofilm formation on catheters implanted in mice infected with E. coli at the incision site when applied as a coating on the catheters. CAP 3 (40 mg/kg) also reduces bacterial load in E. coli-infected wounds in mice. It is cytotoxic to A459 cells (IC50 = 56.4 μM) and has hemolytic activity against human red blood cells with a 50% lysis (HC50) value of 48 μM.