Injury of Escherichia coli K12 by hydrostatic pressure treatment with rapid decompression

We previously found that hydrostatic pressure treatment combined with a rapid decompression (about 2 ms; RD treatment) had a higher bactericidal effect than that with a slow decompression (about 30 s; SD treatment). To further improve the bactericidal efficiency, it is important to make clear the mechanistic aspects of the RD treatment. Therefore, in the present study we tried to detect the injury of Escherichia coli K12 cells using the differential plating method with selective and non-selective agar plates after the SD and RD treatments at 300 MPa and 25°C. The results obtained suggested that the RD treatment had no additional effect on reducing the cellular ability to synthesize essential components. However, the RD treatment accelerated the damages to cell envelope including outer membrane and cytoplasmic membrane compared to the SD treatment. Therefore, it was expected that the envelope damages were one of the major targets of the RD treatment.