Detection of High Hydrostatic Pressure Injured Cells of Escherichia coli on Desoxycholate Agar

Abstract

Detection of cells of Escherichia coli injured by high hydrostatic pressure treatment on Desoxycholate Agar (DESO) was investigated. Cell suspensions were treated by high hydrostatic pressure at 100 to 400MPa, 25°C for 10 to 30min. As pressure and pressurization period increased, surviving cells decreased. Colonies were detected on nonselective Tryptic Soy Agar (TSA) under all tested conditions. However, surviving cells on DESO were significantly lower than on TSA, and colonies could not be detected on DESO when the cells were pressurized at 300 to 400MPa for 20 to 30min. The cells that could grow only on TSA were regarded as injured cells, and were sensitive to desoxycholic acid and neutral red in DESO. A Double layer method (DESO overlaid on TSA) was effective for detecting the injured cells compared with DESO alone.