Damage Effects on Bacille Calmette-Guerin by Low-Frequency, Low-Intensity Ultrasound A Pilot Study

Objectives-To perform an in vitro experimental study of the possible damage effects on Bacille Calmette-Guerin (BCG) by low-frequency (42-kHz) ultrasound (US) irradiation at low spatially and temporally averaged intensities and different exposure times. Methods-A 2-mL BCG suspension was added to the wells of a 24-well cell culture plate. Then the samples were randomly divided into 4 groups, each group including 3 wells, with group 1 as a control group and groups 2, 3, and 4, as US treatment groups. The samples for groups 2, 3, and 4 were irradiated with US at 0.13 W/cm(2) for 5 minutes, 0.13 W/cm(2) for 15 minutes, and 1.53 W/cm(2) for 15 minutes, respectively. After irradiation, the temperature, ratio of damage, and structure of the bacteria were examined. The cavitation effect of the device was detected by the passive cavitation detection method. Results-After US irradiation at the different doses (intensity and exposure time), no significant temperature change was found in all sample suspensions. The ratio of bacterial damage tested by flow cytometry and the optical density of the suspensions as assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric method showed that the US-irradiated groups were significantly different from the control group. The BCG damage ratio reached 28% at the intensity of 1.53 W/cm(2). Transmission electron microscopic results showed that the bacterial structure of BCG could be destroyed by low-frequency, low-intensity US. Conclusions-Low-frequency, low-intensity US can cause acute injury to BCG, and the degree of injury is closely correlated with the US dose applied.