The effects of low-frequency ultrasound on Staphylococcus epidermidis

Low frequency ultrasound (LFUS) significantly enhances skin permeability to a variety of drugs; however, its bacterial effects have not been well stud ied. Staphylococcus epidermidis organisms were grown and standardized to 10 (5) cfu/ml 24 h prior to investigation and suspended in normal saline. LFUS was applied with two probes immersed in the bacterial suspensions over a r ange of suspension volumes, intensities, and exposure times. The suspension temperature was measured, and a sample was removed, streaked onto blood ag ar plates, and incubated at 37 degrees C for 24 h. Quantitative bacterial c ounts were then obtained. LFUS resulted in significant reductions in bacter ial counts that correlated with fluid temperature. Probe size and ultrasoun d intensity appeared to affect bacterial counts, but were also correlated w ith temperature. Bacterial growth was minimal with temperatures exceeding 4 5 degrees C. While LFUS can reduce bacterial counts, these conditions have the potential to cause burns in humans.