THE EFFECT OF ULTRASOUND ON ESCHERICHIA-COLI VIABILITY

The effect of continuous-wave ultrasound on the viability of Escherich ia coli HE 101 was assessed using a 20 kHz ultrasonic processor. A sta ndardised cell suspension of fixed concentration was used to investiga te the influence of different physical and environmental conditions on ultrasound susceptibility. Cell viability decreased exponentially wit h time at different intensities of ultrasound. Increasing intensity ca used a decrease in decimal reduction times. Loss of cell viability occ urred primarily from the mechanical effects of ultrasound rather than free radical damage. E. call susceptibility was also shown to vary wit h growth conditions, whereby cells cultivated either on agar or harves ted from the stationary phase of liquid culture were significantly mor e susceptible to ultrasound than an equivalent population obtained fro m the exponential phase of liquid growth. The implication of these res ults is discussed in relation to the use of ultrasound as a novel mean s of bacterial transformation.