A novel chimeric antimicrobial peptide B5PL dual-targets bacterial cell membrane and neutrophils to combat multidrug-resistant bacterial infections.

Methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Klebsiella pneumoniae (MDR-KP) pose severe threats to global public health due to lack of effective therapeutic strategies. Conventional antibacterial agents exhibit limited potency for modulating host immune defense responses. This study designed a novel chimeric antimicrobial peptide B5PL by fusing a truncated bovine β-defensin 5 (B5) domain with a PL-5 derivative peptide (PL). Results showed that B5 exhibited weak direct bactericidal activity but enhanced the phagocytic and bactericidal functions of macrophages in a TLR2/4 receptor-dependent manner. Furthermore, B5PL disrupted the integrity of bacterial membranes, suppressed the transcription of MRSA virulence genes associated with agr quorum sensing system, significantly improved the survival rate of MRSA-infected mice, and alleviated MRSA-caused pathological damage in the lungs and spleen. Notably, B5PL, not PL, exerted time-dependent bidirectional immunomodulation: it boosted IL-6 and CXCL1 production as well as neutrophil recruitment for bacterial clearance in early infection, whereas it lowered TNF-α and IL-6 levels as well as neutrophil counts to drive inflammation resolution at later infection phase. Additionally, B5PL also conferred effective protection against MDR-KP in mice. Collectively, B5PL targets bacterial membranes and neutrophils to exert direct-indirect antibacterial activities and remodel immune homeostasis, representing a novel peptide candidate against MDR bacterial infections.