Chemokines are important mediators of immunological responses during inflammation and under steady-state conditions. In addition to regulating cell migration, some chemotactic cytokines have direct effects on bacteria. Here, we characterized the antibacterial ability of the synthetic oligopeptide CCL1357–75, which corresponds to the carboxyl-terminal region of the human chemokine CCL13. In vitro measurements indicated that CCL1357–75 disrupts the cell membrane of Pseudomonas aeruginosa through a mechanism coupled to an unordered-helicoidal conformational transition. In a murine pneumonic model, CCL1357–75 improved mouse survival and bacterial clearance and decreased neutrophil recruitment, proinflammatory cytokines and lung pathology compared with that observed in untreated infected animals. Overall, our study supports the ability of chemokines and/or chemokine-derived oligopeptides to act as direct defense agents against pathogenic bacteria and suggests their potential use as alternative antibiotics.