Effect of ultrasonic irradiation on bacterial biofilms.

ABSTRACT

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% CO2. 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.