Effect of ultrasound irradiation on bacterial internalization and bacteria-mediated gene transfer to cancer cells. 
The present study demonstrates that ultrasound irradiation can facilitate bacteria-mediated gene delivery (bactofection).  Escherichia coli modified with avidin were employed as a vehicle for delivery of the green fluorescent protein (GFP) gene, a model heterologous gene, into the breast cancer cell line MCF-7.  Avidin-mediated binding of E. coli to MCF-7 cells enhanced the internalization of E. coli by approximately 17%, irrespective of the use of ultrasound irradiation.  Furthermore, the use of ultrasound irradiation increased the internalization by approximately 5%, irrespective of the presence of avidin on the E. coli cell surface.  The percentages of GFP-expressing MCF-7 cells at 24h after bactofection were below 0.5% and 2% for the case with only avidin-modification of E. coli cell surface and only ultrasound irradiation, respectively.  However, combining avidin modification with the ultrasound treatment increased this value to 8%.  Thus, the use of avidin-modified bacteria in conjunction with ultrasound irradiation has potential as an effective strategy for tumor-targeted bactofection.