2.3. LFU Apparatus

LFU apparatus was provided by Beijing Nava Medical Technology. S-LFU and M-LFU had the same frequency and intensity, which were operated at 40 kHz with continuous irradiation at an intensity of 92.36 mW/cm². S-LFU was operated for 5 min, and M-LFU was operated for 5 min (q8h) on K. pneumonia biofilm [8]. Three biofilm disks and 1 mL MHB in the presence of antimicrobial agents were added to each well of a 24-well plate. To avoid the effect of the holder, the same solution was added to the wells around the edge of the 24-well plate. The ultrasonic transducer was placed in a sterile water-filled ultrasonic bath, 7 cm below the 24-well plate [9]. There was no difference in water temperature before and after ultrasound treatment. Figure 1 illustrates the diagram modified from a previous study [10].

Diagram depicting using LFU and antimicrobial agents for the treatment of K. pneumoniae biofilms. Three catheter disks with biofilms were placed into each well of a 24-well plate containing 1 mL of antimicrobial agent solution. Sterile medium was added to the wells around the edge of the 24-well plate, serving as a negative control. LFU was transmitted through the bottom of the plate via sterile water. This study was to investigate the treatment effect of S-LFU or M-LFU in combination with five different types of antimicrobial agents.