Effect of ultrasound irradiation on bacterial internalization and bacteria-mediated gene transfer to cancer cells

•Ultrasound could facilitate the bacteria-mediated gene delivery (bactofection).•Escherichia coli were used as delivery vehicle of GFP gene into cancer cell MCF-7.•Bactofection efficiency was 0.5% when E. coli cell surface was modified with avidin.•Bactofection efficiency was 2% when ultrasound was irradiated.•Bactofection efficiency became 8% by using both avidin-modification and ultrasound.

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 24 h 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.