Inhibitory Mechanism of Metal-Binding Antimicrobial Peptide SIF₄ on Respiratory and Energy Metabolism of Escherichia coli

This study aimed to systematically elaborate on the inhibitory mechanism of metal-binding antimicrobial peptide SIF₄ on the respiratory and energy metabolism of Escherichia coli. By analyzing changes in the metabolic activity, individual and synergistic respiratory inhibition rate, cytoplasmic membrane ion channel ATPase and intracellular ATP level of E. coli after being treated with SIF₄, the effects of SIF₄ on the cell metabolic activity, respiratory metabolic pathway, cytoplasmic membrane ion channel ATPase and intracellular ATP biosynthesis were studied. Results showed that the metabolic activity of E. coli decreased significantly with increasing dose of SIF₄ (P < 0.05), and decreased by 70.41% in the 2 × minimal inhibitory concentration (MIC) group compared with the control group. SIF₄ had good inhibitory effect on the respiration of Escherichia coli, with an inhibition rate of (19.387 ± 0.168)% and (25.222 ± 0.326)% at MIC and 2 × MIC, respectively. The synergistic respiratory inhibition rate of SIF₄ combined with iodoacetic acid was the lowest ((19.982 ± 0.133)%), indicating that SIF₄ could exhibit high antimicrobial activity mainly by inhibiting the glycolysis pathway of E. coli. The activities of cytoplasmic membrane ion channel Na⁺K⁺-ATPase and Ca²⁺Mg²⁺-ATPase decreased after treatment with SIF₄, and this effect was positively correlated with SIF₄ dose and treatment time, but weaker than that of the positive control Triton X-100. As SIF₄ dose and treatment time increased, the intracellular ATP concentration decreased significantly, and after 12 h, the intracellular ATP concentration in the 2 × MIC group was significantly lower than that in the control group but higher than that in the positive control group (P < 0.05). All results confirmed that SIF₄ could exhibit high antimicrobial activity against E. coli by interfering with respiratory metabolism, weakening cytoplasmic membrane ion channel ATPase activity and inhibiting the biosynthesis of intracellular ATP, which can provide theoretical support for the biocontrol of foodborne E. coli.