Abstract: Provided are polypeptides and compositions comprising the polypeptides for use in killing and/or inhibiting growth of Gram-negative bacteria, particularly P. aeruginosa. The polypeptides are contiguous polypeptides (lysocins) that contain an engineered bacteriocin segment that can be translocated through an outer membrane channel of the Gram-negative bacteria, such as Domain I of the S-type poycin from P. aeruginosa bacterocin pyocin S2 (PyS2) linked to a lysin catalytic segment that has peptidoglycan (PG) hydrolase activity. The lysin catalytic segment can be a catalytic segment of GN4 lysin or any other lysin catalytic segment or a hydrolytic enzyme thereof that has PG hydrolase activity.