Abstract: The blood cells of Phascolosoma esculenta were separated by conventional centrifugation. The leukocyte cells in its coelomic fluid were extracted by acetic acid dialysis, and the antibacterial activity of the extracted substances was determined by agar radial diffusion. The antibacterial mechanism of leukocyte antibacterial substances in the coelomic fluid of P. esculenta was analyzed by scanning electron microscopy and the antibacterial substances in the coelomic fluid were preliminarily separated by acid polyacrylamide gel electrophoresis (A-PAGE). The results showed that there was a broad-spectrum antimicrobial activity substance in leukocytes of P. esculenta coelomic fluid, which had broad-spectrum and high-efficiency antimicrobial activity against most Gram-positive bacteria, Gram-negative bacteria and fungi, and the antimicrobial activity of this substance was highly resistant to high temperature. Enzyme activity test showed that antimicrobial substances had certain proteases but no hemolytic characteristics; scanning electron microscope observation showed that the cell walls of bacteria and yeast treated with antibacterial substances were rough, and holes appeared on the surface of some bacteria. The results of A-PAGE electrophoresis separation and agar radial diffusion preliminarily showed that there were two different antimicrobial active substances in the extract of P. esculenta. It was showed that there was a broad-spectrum and high-temperature resistant antibacterial active substance in the coelomic fluid of P. esculenta, which had a certain application prospect.

Key words: Phascolosoma esculenta, antibacterial substances, antimicrobial activity, coelomic fluid, A-PAGE gel electrophoresis