Objective: To study and compare the bactericidal activity of the polypeptide M17

P26 and N1-11 which derives from hunman group ⅡA phospholipase A2 (PLA2

phospholipase A2) in vitro. Method: Peptide M 17(p51-67)

P26 (p99-124)

N1– 11 (p1-11) were synthesized according to the sequence of human GroupⅡA PLA2 amino acid. Six species of bacterial

Gram positive(G+) Staphy 1ococcus aureus

Bacillus subtilis

Enterococcus faecium

Gram negative(G-) Escherichia coli

Acinetobacter baumannii

Bacillus pyocyaneus

were incubated with different concentration of polypeptides at 37℃ for 2.5 hours in a water bath respectively. Then the reaction solution was diluted and agar plates were poured. After 18-24 hours incubation in the thermostated container at 37℃.The colony formed units were counted and the bactericida1 rates were calculated. Result: Regression equation of PLA2M17 bactericidal activity on the G+ bacteria(lococcus aureus

Bacillus subtilis

Enterococcus faecium) were Y=1.464X+3.795(ED50 6.65 mg·L-1)

Y=1.152X+3.419(ED50 23.57 mg·L-1)

Y=0.836X+3.832 (ED50 24.95 mg·L-1). Regression equation of M17 bactericidal activity on the G-bacteria (E. coli

A. baumannii

B. pyocyaneus)were Y=0.877X+4.054(ED50 12.00 mg·L-1)

Y=1.094X+3.371(ED50 30.83 mg·L-1)

Y=1.027X+3.626(ED50 21.77 mg·L-1). PLA2M17 possessed potent bactericidal activity on the G+ bacteria and G-bacteria.Regression equation of N1-11 and P26 bactericidal activity on B. subtilis were Y=0.915X+2.766(ED50 276.39 mg·L-1)

Y=1.389X+1.668(ED50 250.52 mg·L-1). Regression equation of N1-11 and P26 bactericidal activity on E. coli were Y=1.327X+1.437(ED50 484.18 mg·L-1)

Y=0.881X+2.903(ED50 240.02 mg·L-1).N1-11 and P26 possessed strong bactericidal activity of G+ bacteria

but weaker activity of G- bacteria. M17 possessed stronger bactericidal activity than N1-11 and P26 on B. subtilis and E. coli. Conclusion: Peptide M17 derived from human Ⅱ type A PLA2 highly conserve region possesses a strong bactericidal activity

this may be related to the M17 peptide molecules more easily binding to bacteria.