Effect of ultrasonic irradiation on bacterial biofilms

Purpose The purpose of this study was to clarify the effect of ultrasonic irradiation on biofilm produced by Staphylococcus epidermidis ( S. epidermidis ), which causes central venous catheter-related infections. Materials and methods Staphylococcus epidermidis ( S. epidermidis , ATCC 35984 RP 62A) was used in this study. First, biofilm was prepared from S. epidermidis on the bottom of the upper left well of a 6-well plate. Next, the biofilm was irradiated for 24 h with 1-MHz ultrasound (US) in the continuous wave mode to serve as the US irradiation group. The acoustic power irradiated below the bottom of the well was 3.8 mW. As a control (non-US irradiation group), non-irradiated biofilm on the bottom of a 6-well plate was incubated at 37 °C in an atmosphere of 5.0% CO 2. After US irradiation, the bottoms of the wells were stained with 0.1% crystal violet for 60 s. To extract the crystal violet, 99.5% ethanol was added to the wells, and the extracted solutions were measured at an absorbance of 595 nm. Result The absorbance of the US irradiation group was significantly less than that of the non-US irradiation group ( p < 0.01). Conclusion US irradiation can decrease the amount of S. epidermidis biofilm when the duration of US irradiation is sufficiently long even if the acoustic intensity is low.