Antibacterial mechanisms of ethyl acetate extract from endophytic fungi Alternaria alternata against Staphylococcus aureus / 中草药

ABSTRACT

Objective To investigate the effect of ethyl acetate extract (B06e) from fermentation liquid of an endophytic fungus Alternaria spp. on the cell membrane integrity and the permeability of Staphylococcus aureus. Methods The minimum inhibitory concentration (MIC) of B06e against S. aureus was measured by double dilution method; The changes of electric conductivity of bacterial culture, A260 and A280 before and after treated by B06e were analyzed, respectively. Besides, the changes of cell membrane permeability before and after by B06e was measured by flow cytometry. The effect of B06e on the cell membrane structure was investigated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Results The results showed that MIC value of B06e against S. aureus was 50 μg/mL. The conductivity of 3 × MIC treatment group was 1.06 times of the value of the control group; after treatment of B06e, the values of A260 and A280 were significantly higher than those of the control group The beta-galactosidase activity of 3 × MIC treatment group was 9.43 times more than the value of the control group; Flow cytometry analysis showed that 3 × MIC treatment group by propidium iodide (PI) staining of positive cells was 47.63 times more than the control group; SEM and FT-IR analysis showed that the structure of bacterial cell changed after B06e treatment. Conclusion B06e can kill S. aureus cell by increasing the permeability of its cell membrane and destroy cell membrane integrity.