Cells were treated with either 0.5 × 109/mL PA or PA-MSHA for 24 and 48 hours. They were then washed in twice in phosphate-buffered saline (PBS). Cells were fixed in glutaraldehyde for 2 hours, washed three times with PBS, and then fixed in osmium tetroxide for 2 hours. The samples were washed three times in PBS, dehydrated in a stepwise gradient of ethanol, and then embedded in resin. Samples were sectioned, stained, and imaged using a Hitachi Transmission Electron Microscope (Hitachi, Japan).