Abstract

Antimicrobial peptides are documented as having a crucial role in innate immune response. Many reports have studied antimicrobial peptides from the crocodile. Thus, the antimicrobial activity of liver protein extract from Crocodylus siamensis was examined. Our results show that P50 and P80, partially purified crocodile liver protein extract at 45 mg/ml, can inhibit gram-positive bacteria with the highest percentages of inhibition at 48.22 % and 37.54 % respectively, while gram-negative bacteria could be inhibited at 47.31 % and 35.32 %, respectively. However, only P80 was selected for further phagocytosis activity investigation since it showed low cytotoxicity in the macrophage cell line. The results show that P80 can kill bacteria by an intracellular killing process in phagocytic cells of macrophages in a dose-dependent manner. Moreover, the internalization of phagocytosis activity of macrophages was assayed using fluorescein isothiocyanate-labeled Escherichia coli and flow cytometry. The results reveal that P80 can degrade bacteria by inducing phagosome formation in a time and dose-dependent manner (200-800 μg/ml). In these findings, the liver protein extract of Crocodylus siamensis had an enhancing effect on macrophage RAW 264.7 cells in the phagocytosis process.