| Allium tenuissimum flower essential oil,extracted from Allium tenuissimum flower,is a kind of natural volatile oil with antimicrobial property.This study aims to investigate the chemical characterisations of Allium tenuissimum flower essential oil and the antibacterial actions of its two main compounds(allyl methyl disulfide and dimethyl trisulfide)against three pathogenic bacteria(Escherichia coli,Staphylococcus aureus and Listeria monocytogenes).The results of this investigation are as follows:(1)Allium tenuissimum flower essential oil was extracted from the fresh Allium tenuissimum flower by hydro-distillation method with ultrasonic assistance.Its antibacterial activity was determined against Escherichia coli,Staphylococcus aureus and Listeria monocytogenes by diameters of the inhibition zone,and its chemical compositions were detected by gas chromatography-mass spectrometry(GC-MS).Escherichia coli treated with Allium tenuissimum flower essential oil had the highest diameter of the inhibition zone(15.2 mm)among the three strains.GC-MS analysis revealed that dimethyl trisulfide(35.06 %)and allyl methyl disulfide(19.68 %)were the main compositions of the essential oil.(2)Minimum inhibitory concentrations of allyl methyl disulfide and dimethyl trisulfide against Escherichia coli were both 0.7 mg/m L,and minimum bactericidal concentrations of these two compounds were both 1.4 mg/m L.Aliquots(1.4 mg/m L)of allyl methyl disulfide(dimethyl trisulfide)rigorously damaged surface structure and cytomembranes of Escherichia coli via images of atomic force microscopy and changes of β-galactosidase,and caused the leakage of cellular nucleic acids from the cells.Moreover,the intensities of DNA and protein bands for the cells were significantly decreased after treated with these two compounds.ATPase activities(3.75 and 1.97U/mg prot)of the cells treated with allyl methyl disulfide(1.4 mg/m L)and dimethyl trisulfide(1.4mg/m L)were distinctly lower than activity of the control(6.05 U/mg prot).Moreover,allyl methyl disulfide(1.4 mg/m L)and dimethyl trisulfide(1.4 mg/m L)inactivated 84.20 % and 90.76 %respiratory-chain dehydrogenase for the cells,respectively.(3)Minimum inhibitory concentrations of allyl methyl disulfide and dimethyl trisulfide against Staphylococcus aureus were 1.5 mg/m L and 3.0 mg/m L,respectively.Minimum bactericidal concentrations of allyl methyl disulfide and dimethyl trisulfide were 3.0 mg/m L and6.0 mg/m L,respectively.The images of atomic force microscopy revealed that 3.0 mg/m L allyl methyl disulfide and 3.0 mg/m L dimethyl trisulfide destroyed the cellular morphologies of Staphylococcus aureus.The leakage of cellular β-galactosidase and nucleic acids showed the damage effects of these two compounds on bacterial cytomembranes.The DNA and protein bands of the cells treated with these two compounds(3.0 mg/m L and 6.0 mg/m L)were almost disappeared.Cellular ATPase activities decreased from 4.65 U/mg prot to 0.54 U/mg prot and 4.65U/mg prot to 2.11 U/mg prot with the increases of allyl methyl disulfide and dimethyl trisulfide concentration from 0 to 6.0 mg/m L,respectively.Furthermore,high concentrations(6.0 mg/m L)of allyl methyl disulfide and dimethyl trisulfide decreased the activities of respiratory-chain dehydrogenase by 28.2 % and 27.3 %,respectively.(4)Minimum inhibitory concentrations of allyl methyl disulfide and dimethyl trisulfide against Listeria monocytogenes were both 1.0 mg/m L,and minimum bactericidal concentrations of these two compounds were both 2.0 mg/m L.The morphologies of the cells treated with 2.0 mg/m L allyl methyl disulfide and 2.0 mg/m L dimethyl trisulfide were seriously damaged.Aliquots(4.0mg/mL)of allyl methyl disulfide(dimethyl trisulfide)caused 41.7 %(30.5 %)relative release ofβ-galactosidase from bacterial cells.Moreover,allyl methyl disulfide and dimethyl trisulfide also led to the leakage of nucleic acids and proteins from the cells of Listeria monocytogenes.The brightness of DNA bands of allyl methyl disulfide and dimethyl trisulfide treated Listeria monocytogenes were lower than the control.ATPase activities of the cells treated with high concentrations(4.0 mg/m L)of allyl methyl disulfide and dimethyl trisulfide were 0.52 and 0.55U/mg prot,which were greatly lower than the control(3.05 U/mg prot).Additionally,Aliquots(4.0mg/m L)of allyl methyl disulfide and dimethyl trisulfide decreased the activities of respiratory-chain dehydrogenase by 82.6 % and 87.0 %,respectively.These results demonstrated allyl methyl disulfide and dimethyl trisulfide exhibited antibacterial activity against Escherichia coli,Staphylococcus aureus and Listeria monocytogenes via destructions of cytomembranes and biomacromolecules and inactivation of metabolic enzymes in bacterial cells.Thus,allyl methyl disulfide and dimethyl trisulfide had the capacity to be used as bacteriostatic agents to prevent bacterial growth. |
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