ULTRASONIC ENHANCEMENT OF ANTIBIOTIC ACTION ON GRAM-NEGATIVE BACTERIA

The effect of gentamicin upon planktonic cultures of Pseudomonas aerug inosa, Escherichia coli, Staphylococcus epidermidis, and Staphylococcu s aureus was measured with and without application of 67-kHz ultrasoni c stimulation. The ultrasound was applied at levels that had no inhibi tory or bactericidal activity against the bacteria. Measurements of th e MIC and bactericidal activity of gentamicin against planktonic cultu res of P. aeruginosa and E. coli demonstrated that simultaneous applic ation of 67-kHz ultrasound enhanced the effectiveness of the antibioti c. A synergistic effect was observed and bacterial viability was reduc ed several orders of magnitude when gentamicin concentrations and ultr asonic levels which by themselves did not reduce viability were combin ed. As the age of the culture increased, the bacteria became more resi stant to the effect of the antibiotic alone. Application of ultrasound appeared to reverse this resistance. The ultrasonic treatment-enhance d activity was evident with cultures of P. aeruginosa and E. coli but was not observed with cultures of gram-positive S. epidermidis and S. aureus. These results may have application in the treatment of bacteri al biofilm infections on implant devices, which infections are usually more resistant to antibiotic therapy.