Injury and Recovery of Escherichia coli Cells in Phosphate-buffered Saline after High Hydrostatic Pressure Treatment

Abstract

Escherichia coli cells suspended in phosphate-buffered saline (PBS) were treated by high hydrostatic pressure (HHP; 400 – 600 MPa) at 25 °C for 10 min and then stored at 5 – 25 °C. When treated at 600 MPa, the cells were inactivated lethally. Treatment at 400 and 500 MPa reduced viable cell counts by approximately 7 and 8 log, respectively. Viable counts of cells treated at 400 or 500 MPa increased obviously during storage at 15 and 25 °C, whereas they did not increase at 5 and 10 °C. Meanwhile, healthy E. coli cells inoculated to a heat-killed dead cell suspension in PBS showed drastic growth during storage at 15 and 25 °C, but no growth at 5 and 10 °C. Therefore, the obvious increase in viable counts of HHP-treated cells might be attributed to their cannibalism of the dead cells.