How to improve instrument disinfection by ultrasound

Ultrasound technologies have a wide range of hospital and dental applicatio ns which include cleaning and disinfection of surgical and dental instrumen ts. We measured the germicidal efficacy of sonication, with or without chem ical disinfectants, in an ultrasonic bath delivering a frequency of 35 kHz and an intensity of 0.66 W/cm(2). Cultures of Staphylococcus aureus, Pseudo monas aeruginosa and Candida albicans were exposed to ultrasound and to an amine-based disinfectant in non-bactericidal concentrations. Ultrasonicatio n for 60 min alone did not cause a significant killing of the bacteria and yeast. However, we were able to show that sonication can act as a powerful synergistic agent to increase the cidal efficacy of the disinfectant agains t S. aureus and P aeruginosa. C. albicans was more resistant to the combina tion of ultrasound and chemical disinfection. The key role in the action of ultrasound in cleaning of instruments and perhaps in enhanced disinfection is played by cavitation phenomena. The distribution of cavitations in an u ltrasonic bath is not homogenous. We found a similar synergistic effect of ultrasound and disinfectant in positions with low cavitation. The synergist ic effect was not reduced inside rubber tubes. Before ultrasound can be acc epted as an integral part of the cleaning and disinfection process of medic al instruments, the influence of intensity and frequency of sonication and the effects of cavitation must be clarified. (C) 2001 The Hospital Infectio n Society.