Research conducted by I Ketut Putra, I Made Satriya Wibawa, and I Ketut Sukarasa reveals that exposure to ultrasonic waves in the frequency range of 50–65 kHz significantly increases the mortality of both Gram-positive and Gram-negative bacteria, particularly at higher frequencies and shorter exposure distances.
Ultrasonic waves as an alternative approach to bacterial control
Bacterial control has traditionally relied on chemical agents, heat treatment, or antibiotics. However, these methods often raise concerns related to chemical residues, material damage, and growing antimicrobial resistance. In this context, ultrasonic technology offers a physical, non-chemical approach that minimizes such risks.
Ultrasonic waves are sound waves with frequencies above 20 kHz, beyond the range of human hearing. When propagated through a medium, these waves generate intense mechanical vibrations that can exert physical stress on bacterial cells.
Designing an ultrasonic generator in a physics laboratory
In this study, the researchers designed an ultrasonic generator using a piezoelectric transducer capable of producing stable ultrasonic waves within the 50–65 kHz frequency range. The electronic circuit was built using a multivibrator system and signal amplification to ensure sufficient ultrasonic energy reached the bacterial samples.
The experiments involved Gram-positive bacteria and Gram-negative bacteria, two major bacterial groups distinguished by differences in their cell wall structures. These structural differences are known to influence bacterial resistance to physical stress.
How the experiment was conducted
Bacterial suspensions were exposed to ultrasonic waves for 10 minutes, with variations in frequency and exposure distance. After irradiation, the bacteria were cultured on nutrient media to determine the number of surviving colonies. Mortality rates were calculated by comparing colony counts before and after ultrasonic exposure.
Microscopic observations using Gram staining techniques were also performed to examine changes in bacterial cell morphology.
Higher frequencies lead to higher bacterial mortality
The results demonstrate a consistent pattern: increasing ultrasonic frequency leads to higher bacterial death rates for both Gram-positive and Gram-negative bacteria.
Key findings of the study include:
- For Gram-positive bacteria, exposure at 50 kHz resulted in mortality rates of approximately 34–42 percent, increasing to over 43 percent at 65 kHz.
- Gram-negative bacteria showed higher sensitivity, with mortality rates exceeding 60 percent at 65 kHz.
- Exposure distance played a critical role, as closer proximity to the ultrasonic source produced higher mortality rates.
Microscopic analysis revealed that ultrasonically treated bacterial cells exhibited cell shrinkage, cracked cell walls, and lysis, while untreated bacteria retained normal cellular structures.
Why Gram-negative bacteria are more vulnerable
According to the researchers, the stronger response observed in Gram-negative bacteria is linked to their thinner cell wall structure, which makes them more susceptible to mechanical stress and intense vibrations generated by ultrasonic waves.
The ultrasonic energy induces mechanical pressure that can cause protein coagulation and nucleic acid damage, ultimately leading to bacterial cell death.
Implications for health, food safety, and sanitation
These findings suggest that ultrasonic generators have strong potential as non-chemical sterilization technologies. Possible applications include:
- medical instrument sterilization,
- food processing and safety systems,
- bacterial control in water treatment and sanitation.
Challenges and future research directions
Despite promising results, the researchers emphasize that further studies are needed to optimize ultrasonic frequencies above 65 kHz, vary exposure duration, and test the system on different microbial species.
Additional research is also required to assess energy efficiency, operational stability, and long-term safety before large-scale implementation in industrial and biomedical settings.
Author profiles
• I Ketut Putra – Physics researcher at Udayana University, specializing in physical instrumentation and ultrasonic applications.
• I Made Satriya Wibawa – Physics lecturer at Udayana University, with expertise in electronics and applied physics.
• I Ketut Sukarasa – Physics lecturer at Udayana University, focusing on applied physics and scientific instrumentation.
Research source
Putra, I. K., Wibawa, I. M. S., & Sukarasa, I. K. (2025). The Role of Ultrasonic Generators as Killers of Gram-Positive and Gram-Negative Bacteria.Formosa Journal of Science and Technology, Vol. 5 No. 1, pp. 1–15.
Official URL: https://traformosapublisher.org/index.php/fjst
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