Abstract：Defensins are antimicrobial peptides which play important roles in the innate immune system of mammals. β-defensin-1(pBD-1) and β-defensin-2(pBD-2) are two defensins of great importance in swine. The information on defensin activity and function is very scarce. To study their antimicrobial and antioxidant activities, pBD-1 and pBD-2 were chemically synthesized, and their antimicrobial activities against eight gram-negative bacteria and three gram-positive bacteria were determined by minimal inhibitory concentration(MIC). The mechanisms of antimicrobial peptide activity were preliminary inquiried by transmission electron microscope, and the antioxidant activities in vitro were also studied. The results showed that pBD-1 had strong inhibition against Escherichia coli EPEC O78:K80 and Bacillus subtilis ATCC 6633, which MIC were both 32 μg/mL and minimal bactericide concentration(MBC) were 32 μg/mL and 128 μg/mL, respectively. But pBD-2 had strong inhibition just against Pseudomonas.aeruginosa CMCC 10104, which MIC was 8 μg/mL and MBC was 32 μg/mL. Transmission electron microscopy results showed that pBD-1 and pBD-2 might kill bacteria through the formation of transmembrane pore. pBD-1 and pBD-2 showed radicals scavenging activities and reducing power. Furthermore, the antioxidative activities of them were stronger when the concentrations were higher within certain concentration ranges. In conclusion, the research results indicated that pBD-1 and pBD-2 not only had antimicrobial activities but also had antioxidant activities in certain extent，and this may provide data base to clarify their biological functions and their development and application in animal husbandry.
