Pap12-6, an antibacterial peptide originating from the first twelve N-terminal amino acids of papiliocin found in P. xuthus larvae, exhibits activity against a range of eight Gram-negative bacteria (e.g., E. coli, P. aeruginosa, S. syphimurium with MIC50s=4-8 µM) and Gram-positive bacteria (e.g., S. aureus, methicillin-resistant S. aureus 3126, B. subtilis, and S. epidermidis with MIC50s=4-8 µM), without compromising the viability of human erythrocytes, mouse RAW 264.7 macrophages, human HaCaT keratinocytes, or human HEK293 kidney cells at 25 µM. It causes membrane depolarization in E. coli at 4 and 8 µM and, upon preincubation at 10 µM, decreases nitrite (NO2-), Tnf-α, and Il-6 secretion in LPS-stimulated RAW 264.7 macrophages. In a murine model, Pap12-6 enhances survival rates and diminishes colony forming units (CFUs) in several organs upon E. coli infection at 10 mg/kg and 1 mg/kg doses, respectively. Additionally, at a 1 mg/kg dose, it lowers serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels, as well as blood urea nitrogen levels in E. coli-induced sepsis, indicating its therapeutic potential for bacterial infections without affecting host cell viability.