Five lytic peptides, cecropin A (CA), cecropin B (CB), magainin I (MI), magainin II (MII) and Shiva-1 (a synthetic analog of CB), were evaluated for their antimicrobial activity against Escherichia coli and two pathogenic bacteria of grape, Agrobacterium tumefaciens and Xylella fastidiosa. Peptides were tested at 0.1, 0.5, 1.0, 5.0 and 10.0 muM concentrations in liquid nutrient medium-based assay to determine their relative efficacy in inhibition bacterial growth. A 24-h incubation of E. coli with the respective lytic peptides revealed that both CA and CB exhibited the highest antibacterial activity and completely inhibiting bacterial growth at concentrations as low as 0.5 muM. In contrast, MI, MII and Shiva-2 had no inhibiting effect on E. coli at the tested concentrations. Both CA and CB at concentrations greater than 0.5 muM were highly effective in inhibiting the growth of Agrobacterium, whereas complete inhibition was observed only at MI, MII and Shiva-1 concentrations greater than 5 muM. Growth inhibition profiles of X. fastidiosa were similar to those of E. coli, although Shiva-1 at 10 muM showed a modest growth inhibition.