Fig. 2

a Antibacterial activity of the SAP against E. coli ATCC 25922, S. typhimurium ATCC 14028, Listeria monocytogenes CGMCC 1.10753 and Bacillus cereus CGMCC 1.932 in three pH environments (mean ± SD, n = 3). Compared to control: * p < 0.05, ** p < 0.01, *** p < 0.001. b Antibacterial activity of the SAP and melittin at pH 6.0 against E. coli ATCC 25922 after incubation with trypsin and chymotrypsin at mass ratios of 2:1, 1:1, 0.5:1 and 0.25:1 (enzyme: peptide), respectively for 1 h at 37 °C (mean ± SD, n = 3). # indicated no colony formation. c Antibacterial activity of the SAP against E. coli ATCC 25922 in the presence of 100 mM and 150 mM NaCl at pH 6.0 (mean ± SD, n = 3) Compared to the control: ** p < 0.01. d Cytoplasmic membrane potential variations of E. coli ATCC 25922 treated by SAP and melittin at different concentrations. e SEM micrographs of E. coli ATCC 25922 treated with 250 μg/mL SAP for 30 min at pH 6.0 or not. f TEM micrographs of E. coli ATCC 25922 treated with 250 μg/mL SAP for 30 min at pH 6.0 or not