observed that ultrasound enhanced the inactivation of B. subtilis spores under PEF; however, no details were given in their published abstract as to the intensity of the ultrasonication treatment, whether it was performed before, during or after PEF, and what the actual levels of inactivation were. inactivated 4-log cycles of B. subtilis spores using 2000 Hz sonication combined with PEF at 30–40 kV/cm.