Abstract
The aim of this study was to compare the antibacterial properties of allyl methyl disulfide and dimethyl trisulfide with the chemical compositions of Allium tenuissimum flower essential oil against Escherichia coli O157:H7. Allium tenuissimum flower essential oil was extracted from fresh Allium tenuissimum flower by hydro-distillation method. Its antibacterial activities against Escherichia coli O157:H7, Staphylococcus aureus and Listeria monocytogenes were determined by diameters of the inhibition zone. Escherichia coli O157:H7 treated with the essential oil had the largest diameter of the inhibition zone (15.2 mm) among the three strains. Allyl methyl disulfide and dimethyl trisulfide were two main compounds of the essential oil, as analyzed by gas chromatography-mass spectrometry. The antibacterial characteristics of these two compounds against Escherichia coli O157:H7 were evaluated by minimum inhibitory and bactericidal concentrations, morphologies, cytomembrane destructions, biomacromolecule contents, and metabolic enzyme activities. Minimum inhibitory concentrations of allyl methyl disulfide and dimethyl trisulfide were both 0.7 mg/mL, and minimum bactericidal concentrations of these two compounds were both 1.4 mg/mL. The images of atomic force microscopy exhibited that the surface structures and cytomembranes of Escherichia coli O157:H7 cells were rigorously damaged by 1.4 mg/mL of allyl methyl disulfide and dimethyl trisulfide, leading to the change of β-galactosidases and the leakage of cellular nucleic acids from the bacterial cells. Moreover, the intensities of deoxyribonucleic acid and protein bands of the bacterial cells were significantly decreased after treated with these two compounds at 1.4 mg/mL. Adenosine triphosphatase activities (3.75 and 1.97 U/mg prot) of the bacterial cells treated with allyl methyl disulfide (1.4 mg/mL) and dimethyl trisulfide (1.4 mg/mL) were distinctly lower than the activity of the control (6.05 U/mg prot). Allyl methyl disulfide (1.4 mg/mL) and dimethyl trisulfide (1.4 mg/mL) inactivated 84.20 % and 90.76 % respiratory-chain dehydrogenase of the bacterial cells, respectively. These results demonstrated that allyl methyl disulfide and dimethyl trisulfide exhibited efficient antibacterial characteristics against Escherichia coli O157:H7 and could be used as natural antibacterial agents in the prevention of Escherichia coli O157:H7 infection.
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