Background: A case of Acinetobacter baumannii  (A. baumannii ), known as gram-negative bacteria, causes a range of nosocomial infections. Due to the continuous detection of multi-drug resistant A. baumannii  in the clinic, there is an urgent need to find alternative therapies, including broad-spectrum antibacterial peptides (AMP). Recently it has been found that the peptide Cec4 has good antibacterial activity against A. baumannii , but the antibacterial mechanism remains elusive.
Materials and methods: The basic structure of Cec4 was analyzed by circular dichroism (CD) spectroscopy, and the potential antibacterial mechanism of Cec4 was detected by flow cytometry, transmission electron microscopy, fluorescence and confocal microscopy. The minimum inhibitory concentration (MIC) of antimicrobial peptides against various A. baumannii  was determinated with broth microdilution techniques. The biofilm formation and the sensitivity detection of biofilms to antimicrobial peptides were detected by crystal violet staining.
Results: In this study, the main secondary structure of the antibacterial peptide Cec4 is α-helix (99.7%) in the hydrophobic environment. Furthermore, after the treatment with Cec4, an amount of leakage of A. baumannii  and the destruction of its cell membrane were detected. Moreover, it was observed that FITC-Cec4 can enter the cell, and more cells were held in the G1 phase with peptide Cec4. However, the DNA binding assay of the peptide Cec4 indicates that the peptide does not target DNA. In addition, peptide Cec4 was superior in reducing adherent biofilms of A. baumannii  compared to conventional antibiotics and has no cytotoxicity.
Conclusion: It is apparent that the antibacterial peptide Cec4 may achieve rapid sterilization by multi-target interaction and presents an attractive therapeutic option for the prevention and control of A. baumannii  infections.
Keywords: antimicrobial peptides, A. baumannii , antibacterial mechanism, cell membrane