Inactivation of Escherichia coli by sonication at discrete ultrasonic frequencies

The sonolytic inactivation of Escherichia coli (E. coli) is reported. The impact of power intensity, dissolved gas and ultrasonic frequency on the germicide effectiveness of sonification has been explored. The inactivation of E. coli exhibits pseudo-first order behavior, and depends moderately on total power and power intensity at a frequency of 20 kHz. The rate coefficients in an oxygenated solution vary from 0.031 to 0.046 min−1 when the power intensity ranges from 4.6 to 74 W cm−2. Inactivation occurs most readily at the highest sound intensity, 74 W cm−2. Three dissolved gases were investigated: oxygen, argon, and an argon/oxygen mixture. The nature of the dissolved gas does not strongly influence the magnitude of the inactivation coefficients which varied from k=0.027 min−1 to 0.047 min−1. Ultrasonic frequency, within the limits of 205–1017 kHz, displays a strong influence on the rate of E. coli inactivation in oxygenated solutions. The rate coefficients vary from 0.030 to 0.078 min−1. The most effective ultrasonic frequency for E. coli innovation is 205 kHz; the rate coefficient (k=0.078 min−1) is greater than the coefficient at 1071 kHz (k=0.030 min−1) by a factor of 2.6 and 358 kHz (k=0.064 min−1) also demonstrates a greater efficiency than either 618 kHz (k=0.041 min−1) or 1017 kHz.