Synergistic Inhibitory Mechanism Of Soybean Globulin Alkaline Peptide And Nisin Against Listeria Monocytogenes

Soybean globulin alkaline peptide(GBAP),isolated from soybean globulin,is a kind of alkaline peptide with antibacterial activity.Nisin,secreted by Lactococcus lactis,is a kind of non-toxic peptide antibiotic.This paper mainly focus on the synergistic antibacterial effects and mechanisms of GBAP and Nisin against L.monocytogenes.The results were shown as follows:(1)The single treatment of GBAP and Nisin both can effectively inhibit the growth of L.monocytogenes.The minimum inhibitory concentration(MIC)of GBAP is 0.2mg/m L,the MIC of Nisin is 0.5 mg/m L.The combination of 0.05 mg/m L GBAP and0.0625 mg/m L Nisin can effectively inhibit the growth of L.monocytogenes,which present the synergistic effect.The bacteriostatic kinetics experiment showed that the antibacterial mechanism of GBAP and Nisin against L.monocytogenes were different.The combination of GBAP and Nisin may made up the deficiency of their respective functions to some extent.(2)Nisin strongly destroyed the cell membrane and morphology of L.monocytogenes cells,leading to significant membrane depolarization and intracellular components leakages.The membrane destruction caused by GBAP was weaken.But GBAP resulted in significant nuclear aggregation,which might target intracellular components.GBAP+Nisin treatment lead to both cell membrane damages and accumulation of nucleic and impedes the closure of cell walls.(3)GBAP disrupt the DNA and proteins synthesis processes of L.monocytogenes,while Nisin only influence the proteins synthesis process.GBAP inhibited the respiratory metabolism of L.monocytogenes by targeting EMP pathway and related key enzymes in the EMP pathway.The destruction of L.monocytogenes cell membrane caused by Nisin also indirectly inhibited the respiratory metabolism.The combination of GBAP and Nisin enhance the inhibitory effect on L.monocytogenes respiratory metabolism.(4)GBAP inactivate the key enzymes in EMP pathway by down-regulating the expressions of related genes.The disruption of cell cycle regulation genes cause by GBAP and Nisin resulted in the abnormal growth of L.monocytogenes.Nisin further inhibited the expression of genes that control the cell wall synthesis of L.monocytogenes.GABP inhibited the expression of genes involved in RNA transcriptionand translation of L.monocytogenes,further inhibited the transcription and protein synthesis extension processes,finally resulted in the protein fragmentation.Nisin only presented the slight effect on the expression of these genes.When GBAP was combined with Nisin,the L.monocytogenes membrane damages caused by Nisin help GBAP enter into the cell,and targeting intracellular substances to exhibit inhibitory effect,which enhances the antibacterial effect on L.monocytogenes.