Physical Science: New Insights and Developments Vol. 4

Ultrasonic waves, which operate at frequencies above the threshold of human hearing, are capable of generating mechanical effects and acoustic cavitation phenomena in liquid media. These effects can induce significant damage to the cellular structures of microorganisms. Although several studies have reported the effectiveness of ultrasonic waves in bacterial inactivation, investigations into the influence of ultrasonic frequency variation on bacterial mortality, particularly in relation to differences in cell wall characteristics, remain limited. This study presents the design and experimental implementation of an ultrasonic generator utilising an IC 555 timer as the source of ultrasonic waves for bacterial inactivation. The developed system operated within a frequency range of 40–65 kHz and was experimentally tested using suspensions of Gram-positive and Gram-negative bacteria with identical initial concentrations. The Gram-positive bacterium used was Staphylococcus aureus, while the Gram-negative bacterium was Escherichia coli. The bacterial suspensions were exposed to ultrasonic waves at different frequencies and irradiation distances for a constant exposure time of 10 minutes. The effectiveness of the ultrasonic treatment was assessed by calculating the percentage of bacterial mortality and the average reduction in bacterial count (CFU/mL). The results indicate that bacterial mortality increases as the ultrasonic frequency rises for both types of bacteria. Under the same irradiation conditions, Gram-negative bacteria consistently showed higher mortality rates than Gram-positive bacteria. For Gram-positive bacteria at 5 cm, mortality increased from 34.3% to 43.5%, while average mortality rose from 42.6 to 65.0 CFU/mL. Gram-negative bacteria showed higher susceptibility, with mortality increasing from 50.3% to 63.6% and average mortality from 49.3 to 96.3 CFU/mL at the same distance. Furthermore, decreasing the irradiation distance improved the efficiency of bacterial inactivation for both bacterial groups. Future studies should focus on measuring ultrasonic power and monitoring temperature changes during exposure to provide a more comprehensive understanding of the inactivation mechanism.