柠檬醛体外抗MRSA活性及其对β-内酰胺类抗生素的增效作用

The in vitro activity and synergistic effect of citral on β-lactam antibiotics against methicillin-resistant Staphylococcus aureus

通过体外抑菌实验评价柠檬醛单独使用以及与3种β-内酰胺类抗生素（阿莫西林、头孢氨苄及头孢吡肟）联合使用对耐甲氧西林金黄色葡萄球菌（Methicillin-resistant Staphylococcus aureus,MRSA）的抑制效果.采用微量稀释法测定柠檬醛与3种β-内酰胺类抗生素的最低抑菌浓度（Minimum inhibitory concentration,MIC）及最低杀菌浓度（Minimum bactericidal concentration,MBC）;用微量棋盘法测定柠檬醛与3种β-内酰胺类抗生素的分级抑菌浓度（Fractional inhibitory concentration,FIC）指数;用分光光度法测定柠檬醛和阿莫西林联合使用后对MRSA生长的抑制效果.结果显示：柠檬醛MIC和MBC分别为695-2 780μg/mL和1 390-2 780μg/mL.联合药敏试验发现柠檬醛与3种β-内酰胺类抗生素联合使用FIC指数集中分布在≤0.5和0.5-1;与单独用药相比,阿莫西林、头孢氨苄和头孢吡肟的MIC_（50）分别降低为原来的1/9、1/15和1/9;1/4 MIC阿莫西林与1/4 MIC柠檬醛联合用药后,显著抑制了MRSA的生长.因此,柠檬醛具有一定的体外抗MRSA活性,与阿莫西林、头孢氨苄和头孢吡肟等β-内酰胺类抗生素联合使用时可增强β-内酰胺类抗生素的活性,降低其用量.

In order to develop alternative treatment for methicillin-resistant Staphylococcus aureus（MRSA） infection, we explored the in vitro activity of citral against MRSA and evaluated the inhibitory effect of citral combined with three kinds of β-lactam antibiotics（amoxicillin, cefalexin, and cefepime） against MRSA. The minimum inhibitory concentration（MIC） and minimum bactericidal concentration（MBC） of citral were determined using 96-well plate dilution method. The microfluidic method was used to determine the fractional inhibitory concentration（FIC） index of citral combined with the three β-lactam antibiotics. The inhibitory effect of citral combined with amoxicillin on the growth curve of MRSA was determined spectrophotometrically. The results showed that the MIC and MBC of citral were 695-2 780 μg/mL and 1 390-2 780 μg/mL, respectively. Combined drug susceptibility test showed that the FIC index of citral combined with the three β-lactam antibiotics mainly distributed in 0.5-1 and 0.5; compared to when the β-lactam antibiotics were used alone, the MIC_（50） of the three antibiotics in combination with citral was reduced to 1/9, 1/15, and 1/9 of the original value, respectively. The combined use of citral and amoxicillin significantly inhibited the growth of MRSA. Taken together, these findings suggest that citral exhibits anti-MRSA activity in vitro and obvious synergistic antibacterial activity with β-lactam antibiotics and indicate its potential in the development of natural anti-MRSA drugs.