The parameters influencing outer membrane permeability of Pseudomonas aeruginosa PAO1 under high hydrostatic pressure were quantified and optimized, using fusion between a specific A1 gamma peptidoglycan-binding domain and green fluorescent protein (PBD-GFP). Based on the obtained data, optimal conditions were defined to assess the synergistic bactericidal action between high hydrostatic pressure and peptidoglycan hydrolysis by bacteriophage-encoded endolysins KZ144 and EL188. Under high hydrostatic pressure, both endolysins show similar inactivation of P. aeruginosa as the commonly used hen egg white lysozyme or slightly higher inactivation in the case of EL188 at 150 and 200 MPa. The partial contribution of pressure to the bacterial inactivation increases with higher pressure, while the partial contribution of the enzymes is maximal at the onset pressure of outer membrane permeabilization for the PBD-GFP protein (175 MPa). This study's results demonstrate the usefulness of this approach to determine optimal synergy for hurdle technology applications.