Effect of incubation temperature after high hydrostatic pressure treatment of Escherichia coli on the detection of injured populations

Abstract

ABSTRACT Escherichia coli in phosphate-buffered saline was treated with high hydrostatic pressures (HHPs) of 400, 500, and 600 MPa at 25 °C for 10 min. The cell suspension was then plated on nonselective agar and incubated at 20, 25, 30, 35, 37, and 40 °C to study the effect of the incubation temperatures on the detection of HHP-injured populations. The number of detected cells was maximum when incubated at 25 °C for 72 h. Cold storage at 4 °C for 7 d after HHP-treatment improved the detection efficacies of incubations at 30–40 °C, implicating increased tolerance of HHP-injured cells against the mild heat. Combined incubation at 25 °C for more than 6 h with subsequent incubation at 35 °C shortened total incubation period from 72 h to 24 h while achieving the maximized colony number obtained by the incubation at 25 °C for 72 h.