Abstract:

Cavitation is known to have biocidal effect upon micro-organisms. The work presented here considered the impact of transient cavitation at elevated hydrostatic pressures as a means to improve the biocidal efficacy of otherwise mild disinfectant solutions. Cultures of Bacillus stearothermophilus and Bacillus subtilis were exposed to a mild isopropyl alcohol-based disinfectant for 15 to 18 minutes, which resulted in negligible cell reduction. Spores from the same cultures were exposed to the disinfectant for 15 to 18 minutes while being cavitated for one minute at a frequency of 24 kHz, and at ambient pressure, with an estimated energy density of 70 watts per liter. This achieved cell reduction of approximately 2%. Spores from the same cultures were exposed to the same cavitation field but at a hydrostatic pressure of approximately 210 kPa. The pressure was selected to exploit ``the anomalous depth effect'' for enhanced transient cavitation. These conditions achieved cell reduction of approximately 90% after 1 minute of cavitation exposure. The results are suggestive of more efficient means of sterilizing the burgeoning numbers of heat sensitive surgical instruments.