THE EFFECT OF ULTRASONIC FREQUENCY UPON ENHANCED KILLING OF PSEUDOMONAS-AERUGINOSA BIOFILMS

It is widely recognized that the bacteria sequestered in a biofilm on a medical implant are much more resistant to antibiotics than their pl anktonic counterparts. Recent studies have shown that application of a ntibiotic along with low power ultrasound significantly increases the killing of planktonic bacteria by the antibiotic. Herein is reported a similar application of antibiotic and ultrasound to sessile bacteria in biofilms of Pseudomonas aeruginosa on a polyethylene substrate. Bio film viability was measured after exposure to 12 mu g/ml gentamicin su lfate and 10 mW/cm(2) ultrasound at frequencies of 70 kHz, 500 kHz, 2. 25 MHz, and 10 MHz. The results indicate that a significantly greater fraction of the bacteria was killed by gentamicin when they were subje cted to ultrasound. However, ultrasound by itself did not have any del eterious effect on the biofilm viability. In addition, lower-frequency insonation is significantly more effective than higher frequency in r educing bacterial viability within the biofilm. The possible mechanism s of synergistic action are discussed.