Physiological effects of high hydrostatic pressure treatments on Listeria monocytogenes and Salmonella typhimurium

Abstract

The effect of a high hydrostatic pressure treatment on the Gram-positive Listeria monocytogenes strain Scott A and the Gram-negative Salmonella typhimurium strain Mutton (ATCC13 311) has been determined in stationary phase cell suspensions. Pressure treatments were done at room temperature for 10 min in sodium citrate (pH 5·6) and sodium phosphate (pH 7·0) suspension buffers. Increasing pressure treatments resulted in an exponential decrease of cell counts. Salmonella typhimurium suspended at low pH was more sensitive to pressure treatments. Progressive morphological changes were evident with the pressure increase. Cell lysis only appeared with the highest pressure treatments. Cell volume was not affected by pressure treatment. A progressive decrease of dpH (pH in -pH out ), intracellular potassium and ATP contents was demonstrated with the pressure increase. A parallel lowering of membrane potentials was measured.

Influence of high-pressure–low-temperature treatment on the inactivation of Bacillus subtilis cells

“…10 2 ml À 1 ) since the initial inoculum was 10 7 -8 cfu/ml and contained up to 10 2 cfu/ml spores (see Materials and methods). These results are in good agreement with the pressure resistance experiment on Listeria monocytogenes performed at 20 -C (Tholozan, Ritz, Jugiau, Federighi, & Tissier, 2000).…”

Morphological and Physiological Characterization of Listeria monocytogenes Subjected to High Hydrostatic Pressure

“…In addition, SEM examination showed that the 400-MPa treatment could induce some cell disruptions. The same was observed with Salmonella in other studies (13,28). Whatever the method used, these results show that even if the pressure treatment leads to total inactivation of the population, individual cells retain their morphological characteristics.…”

Evaluation of Structural Changes Induced by High Hydrostatic Pressure in Leuconostoc mesenteroides

“…Longer heating times resulted in a decrease of cells with surface blisters. Deformations on the surface of L. monocytogenes cells, described as bud scars, pimples, and swellings, have been reported as a result of pressure treatment at 400 MPa and 20°C for 10 min (29,33). Both studies reveal an increase in the number of deformations at pressures between 275 and 400 MPa.…”