Abstract: The immunized hemolymph was produced from Musca domestica larvae by the induction of injury and bacteria infection. The antibacterial peptide was purified by means of boiled water bath, dialysis and concentration, Tricine-SDS-PAGE preparation, retrieval and renaturing of peptides. The result of amino acid analysis showed that the molecule weight of antibacterial peptide (MDL-2) was 11 kD. It contained abundant Pro, Gly and alkaline amino acids, which had activity against Gram-positive bacteria, S. aureus and Gram-negative bacteria, E. coli. Electrophrosis was proved an effective way to prepare antibacterial peptides. The circular dichroism spectra of antibacterial peptide MDL-2 in different solutions was analyzed. The antibacterial mechanism was primarily studied through observing permeability and morphological changes of bacterial cells. The results showed that MDL-2 caused a series of pathological changes to bacteria. Transmisson electron microscopy showed that MDL-2 was located in the plasma membrane. MDL-2 combined with bacterial cells by static electricity gravitation at the early stage, then resulted a flexible amphipathic spatial conformation, interacted with the plasma membrane, disturbed ordered arrangement of membrane lipid and changed permeability, thus irregular holes appeared on the plasma membrane and the cytoplasmic contents leaked out, so that metabolism system of bacteria was disturbed. Finally, bacteria were disintegrated into small fragments and died.

Key words: Musca domestica, antibacterial peptide, electrophoretic preparation, ultrastructure, antibacterial mechanism