厚鳞柯叶水提物对耐甲氧西林金黄色葡萄球菌的抑菌机理

Antibacterial mechanism of aqueous extract of Lithocarpus pachylepis leaf against methicillin-resistant Staphylococcus aureus

  • 摘要: 【目的】明确厚鳞柯叶水提物(Aqueous extract of Lithocarpus pachylepis leaf, AELL)对耐甲氧西林金黄色葡萄球菌 (Methicillin-resistant Staphylococcus aureus, MRSA)的抑菌效果及其作用机理,为开发安全高效、低毒环保、无残留的抗MRSA药物提供理论依据。【方法】采用微量肉汤稀释法、平板菌落计数法分别测定AELL对MRSA的最小抑菌浓度 (MIC)和最小杀菌浓度 (MBC),以比浊法绘制AELL处理后MRSA的生长曲线,并通过酶标仪测定、流式细胞仪及扫描电镜等测定AELL处理后MRSA生物被膜清除作用、纤维蛋白原黏附率、呼吸代谢活力、可溶性蛋白含量、DNA含量、细胞周期分布、细胞凋亡率、胞内活性氧(ROS)水平及其形态结构特征的变化情况。【结果】 AELL可能通过影响MRSA对数生长期而发挥抑制或杀灭作用,其MIC和MBC均为0.15625 mg/mL。与空白对照组相比,经AELL处理后MRSA的生物被膜含量明显下降;随着AELL处理浓度的增加, MRSA相对黏附率呈逐渐下降趋势,从47.486%下降到5.440%。随着AELL处理时间的延长, MRSA的呼吸代谢活力逐渐降低,且呼吸链脱氢酶活性明显低于空白对照组,说明AELL可能是通过抑制MRSA呼吸链脱氢酶活性促使菌株处于死亡甚至呈破碎状态。经AELL处理后,MRSA可溶性蛋白呈明显下降趋势,还扰乱MRSA细胞周期分布,使其停滞在S期,同时抑制DNA合成; MRSA的细胞凋亡率和胞内ROS水平均随AELL浓度的增加而呈逐渐上升趋势; MRSA的形态结构不规则、萎缩、畸形,细胞塌陷,细胞间隙出现裂痕,细胞壁严重弯曲、变形。【结论】 AELL具有开发成抗MRSA兽药、植物杀菌剂的潜力,其抑菌机理是通过清除MRSA生物被膜,降低其对纤维蛋白原黏附力,抑制蛋白和DNA生成,阻碍呼吸代谢,延缓细胞繁殖周期及促进菌体内脂质过氧化等,从而导致菌体细胞凋亡。

     

    Abstract: 【Objective】 To make clear antibacterial effect and mechanism of aqueous extract of Lithocarpus pachylepis leaf(AELL)against methicillin-resistant Staphylococcus aureus(MRSA),so as to provide theoretical basis for developing safe,efficient,environmentally friendly,low-toxic and residue-free anti-MRSA drugs.【Method】 Minimal inhibitory concentration(MIC)and minimal bactericidal concentration(MBC)of AELL against MRSA were measured by broth microdilution method and plate colony counting method.Growth curve of MRSA after AELL treatment was drawn by turbidimetry.Biofilm clearance,fibrinogen adhesion rate,respiratory metabolism activity,soluble protein content,DNA content,cell cycle distribution,apoptosis rate,intracellular reactive oxygen species(ROS)level and morphological and structural characteristics of MRSA after AELL treatment were measured by microplate reader,flow cytometry and scanning electron microscope.【Result】AELL could inhibit or kill MRSA by affecting its logarithmic growth phase,and its MIC and MBC were both 0.15625 mg/mL.Compared with the blank control group,the biofilm content of MRSA after AELL treatment decreased significantly.With the increase of AELL concentration,relative adhesion rate of MRSA decreased gradually from 47.486% to 5.440%.With the prolongation of AELL treatment time,respiratory metabolic activity of MRSA decreased gradually,and respiratory chain dehydrogenase activity was significantly lower than that of the blank control group,which indicated that AELL might inhibit respiratory chain dehydrogenase activity of MRSA to kill or break the strain.After AELL treatment,soluble protein of MRSA decreased obviously,and distribution of MRSA cell cycle was disturbed,making MRSA stay in S phase and inhibiting DNA synthesis;apoptosis rate and intracellular ROS level of MRSA increased gradually with the increase of AELL concentration;morphological structure of MRSA were irregular,atrophied and deformed,the cells collapsed,the intercellular cracks appeared,and the cell walls were severely bent and deformed.【Conclusion】 AELL is potential to be developed as an anti-MRSA veterinary drug and botanical fungicide.Its bacteriostasis mechanism is to remove MRSA biofilm,reduce its adhesion to fibrinogen,inhibit protein and DNA production,hinder respiratory metabolism,delay cell reproduction cycle and promote lipid peroxidation in bacteria,leading to apoptosis of bacteria.

     

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