Synergistic bactericidal effect of low-frequency and low-intensity ultrasound combined with levofloxacin-loaded nanoparticles on M. smegmatis in macrophages

<title>Abstract</title> Purpose Tuberculosis is a highly infectious disease caused by Mycobacterium tuberculosis (Mtb) which often parasites in macrophages. The present study was to investigate the bactericidal effect and underlying mechanisms of low-frequency and low-intensity ultrasound (LFLIU) combined with levofloxacin-loaded nanoparticles (LEV-NPs) on M. smegmatis (a surrogate of Mtb )in macrophages. Methods and results LEV-NPs were prepared by a double emulsification method. The characterization, such as average diameter, zeta potential, polydispersity index and morphology, and in-vitro drug release efficiency of LEV-NPs were investigated. M. smegmatis in macrophages was treated by LEV-NPs combined with 42 kHz ultrasound irradiation at an intensity of 0.13 W/cm 2 for 10 min. The results showed ultrasound could significantly promote phagocytosis of nanoparticles by macrophages ( p &lt;0.05), further ultrasound combined with LEV-NPs could promote the production of macrophage ROS, and the apoptosis rate of macrophages was significantly higher than that of the control ( p &lt;0.05). Transmission electronic microscope showed M. smegmatis cell wall was ruptured, the cell structure was incomplete, and the bacteria received severe damage in the ultrasound combined with the LEV-NPs group. Activity assays showed that ultrasound combined with LEV-NPs exhibited 10-fold higher antibacterial activity against M. smegmatis residing inside macrophages compared with free drug. Conclusion Our data demonstrate that ultrasound combined with LEV-NPs have a great potential to therapy of tuberculosis.